（我发现这些题,答案不一样）16.People can find almost whatever the need at the new shopping mall,______ is always busy at weekends.A.where B.which C.that D.as17.----What do you think of the ties ---- Perfect.But I don't know which is bett_百度作业帮
（我发现这些题,答案不一样）16.People can find almost whatever the need at the new shopping mall,______ is always busy at weekends.A.where B.which C.that D.as17.----What do you think of the ties ---- Perfect.But I don't know which is bett
（我发现这些题,答案不一样）16.People can find almost whatever the need at the new shopping mall,______ is always busy at weekends.A.where B.which C.that D.as17.----What do you think of the ties ---- Perfect.But I don't know which is better,so I'll take ______ of them.A.either B.both C.neither D.none18.----Can David take charge of the international department?----I'm afraid it's _______ his ability.A.beyond B.over C.with D.unde20.----How about _______ Christmas evening party?-----I should say it was _______ success.A.a; a B. a C. 不填 D. 不填28.I wrote a letter to the car rental agency,explaining ______ had happene.A.why B.what C.that D.how
16题打错了吧?应该是 whatever they need 选B 非限制性定语从句17C 两个都好不知道哪个更好因此一个都不买.18A 20B 28B
可以给我解释一下第一题吗？因为我一开始选的是A。
where引导的话 从句缺主语
求 满意回答
好的，谢谢你！
16which表示非限制性定语从句17B Better表示2者比较，所以都买用both18A byond one's ability是超出某人的能力20B the特指，a一次成功泛指 29B 宾语从句希望这一回答对你有所帮助，如满意请点击下面的“选为满意答案”按钮，谢谢您！7 myths about the Challenger shuttle disaster - Technology & science - Space | NBC News
AFP - Getty Images file
These sequential photos show a fiery plume escaping from the right solid rocket booster as the space shuttle Challenger ascends to the sky on Jan. 28, 1986.
By James Oberg
NBC News space analyst
Special to NBC News
Twenty-five years ago, millions of television viewers were horrified to witness the live broadcast of the space shuttle Challenger exploding 73 seconds into flight, ending the lives of the seven astronauts on board. And they were equally horrified to learn in the aftermath of the disaster that the faulty design had been chosen by NASA to satisfy powerful politicians who had demanded the mission be launched, even under unsafe conditions. Meanwhile, a major factor in the disaster was that NASA had been ordered to use a weaker sealant for environmental reasons. Finally, NASA consoled itself and the nation with the realization that all frontiers are dangerous and to a certain extent, such a disaster should be accepted as inevitable.
At least, that seems to be how many people remember it, in whole or in part. That’s how the story of the Challenger is often retold, in oral tradition and broadcast news, in public speeches and in private conversations and all around the Internet. But spaceflight historians believe that each element of the opening paragraph is factually untrue or at best extremely dubious. They are myths, undeserving of popular belief and unworthy of being repeated at every anniversary of the disaster.
The flight, and the lost crew members, deserve proper recognition and authentic commemoration. Historians, reporters, and every citizen need to take the time this week to remember what really happened, and especially to make sure their memories are as close as humanly possible to what really did happen.
If that happens, here's the way the mission may be remembered:
Few people actually saw the Challenger tragedy unfold live on television.
The shuttle did not explode in the common definition of that word.
The flight, and the astronauts’ lives, did not end at that point, 73 seconds after launch.
The design of the booster, while possessing flaws subject to improvement, was neither especially dangerous if operated properly, nor the result of political interference.
Replacement of the original asbestos-bearing putty in the booster seals was unrelated to the failure.
There were pressures on the flight schedule, but none of any recognizable political origin.
Claims that the disaster was the unavoidable price to be paid for pioneering a new frontier were self-serving rationalizations on the part of those responsible for incompetent engineering management — the disaster should have been avoidable.
Myth #1: A nation watched as tragedy unfolded
Few people actually saw what happened live on television. The flight occurred during the early years of cable news, and although CNN was indeed carrying the launch when the shuttle was destroyed, all major broadcast stations had cut away —
only to quickly return with taped relays. With Christa McAuliffe set to be the first teacher in space, NASA had arranged a satellite broadcast of the full mission into television sets in many schools, but the general public did not have access to this unless they were one of the then-few people with satellite dishes. What most people recall as a "live broadcast" was actually the taped replay broadcast soon after the event.
Myth #2: Challenger exploded
The shuttle did not explode in the common definition of that word. There was no shock wave, no detonation, no "bang" — viewers on the ground just heard the roar of the engines stop as the shuttle’s fuel tank tore apart, spilling liquid oxygen and hydrogen which formed a huge fireball at an altitude of 46,000 ft. (Some television documentaries later added the sound of an explosion to these images.) But both solid-fuel strap-on boosters climbed up out of the cloud, still firing and unharmed by any explosion. Challenger itself was torn apart as it was flung free of the other rocket components and turned broadside into the Mach 2 airstream. Individual propellant tanks were seen exploding — but by then, the spacecraft was already in pieces.
Myth #3: The crew died instantly
The flight, and the astronauts’ lives, did not end at that point, 73 seconds after launch. After Challenger was torn apart, the pieces continued upward from their own momentum, reaching a peak altitude of 65,000 feet before arching back down into the water. The cabin hit the surface 2 minutes and 45 seconds after breakup, and all investigations indicate the crew was still alive until then.
What's less clear is whether they were conscious. If the cabin depressurized (as seems likely), the crew would have had difficulty breathing. In the words of the final report by fellow astronauts, the crew “possibly but not certainly lost consciousness,” even though a few of the emergency air bottles (designed for escape from a smoking vehicle on the ground) had been activated.
The cabin hit the water at a speed greater than 200 mph, resulting in a force of about 200 G’s — crushing the structure and destroying everything inside. If the crew did lose consciousness (and the cabin may have been sufficiently intact to hold enough air long enough to prevent this), it’s unknown if they would have regained it as the air thickened during the last seconds of the fall. Official NASA commemorations of “Challenger’s 73-second flight” subtly deflect attention from what was happened in the almost three minutes of flight (and life) remaining AFTER the breakup.
Myth #4: Dangerous booster flaws result of meddling
The side-mounted booster rockets, which help propel the shuttle at launch then drop off during ascent, did possess flaws subject to improvement. But these flaws were neither especially dangerous if operated properly, nor the result of political interference.
Each of the pair of solid-fuel boosters was made from four separate segments that bolted end-to-end-to-end together, and flame escaping from one of the interfaces was what destroyed the shuttle. Although the obvious solution of making the boosters of one long segment (instead of four short ones) was later suggested, long solid fuel boosters have problems with safe propellant loading, with transport, and with stacking for launch — and multi-segment solids had had a good track record with the Titan-3 military satellite program. The winning contractor was located in Utah, the home state of a powerful Republican senator, but the company also had the strengths the NASA selection board was looking for. The segment interface was tricky and engineers kept tweaking the design to respond to flight anomalies, but when operated within tested environmental conditions, the equipment had been performing adequately.
Myth #5: Environmental ban led to weaker sealant
A favorite of the Internet, this myth states that a major factor in the disaster was that NASA had been ordered by regulatory agencies to abandon a working pressure sealant because it contained too much asbestos, and use a weaker replacement. But the replacement of the seal was unrelated to the disaster — and occurred prior to any environmental ban.
Even the original putty had persistent sealing problems, and after it was replaced by another putty that also contained asbestos, the higher level of breaches was connected not to the putty itself, but to a new test procedure being used. “We discovered that it was this leak check which was a likely cause of the dangerous bubbles in the putty that I had heard about," , a member of the Challenger investigation board.
And the bubble effect was unconnected with the actual seal violation that would ultimately doom Challenger and its crew. The cause was an inadequate low-temperature performance of the O-ring seal itself, which had not been replaced.
Myth #6: Political pressure forced the launch
There were pressures on the flight schedule, but none of any recognizable political origin. Launch officials clearly felt pressure to get the mission off after repeated delays, and they were embarrassed by repeated mockery on the television news of previous scrubs, but the driving factor in their minds seems to have been two shuttle-launched planetary probes. The first ever probes of this kind, they had an unmovable launch window just four months in the future. The persistent rumor that the White House had ordered the flight to proceed in order to spice up President Reagan’s scheduled State of the Union address seems based on political motivations, not any direct testimony or other first-hand evidence. Feynman personally checked out the rumor and never found any substantiation. If Challenger's flight had gone according to plan, the crew would have been asleep at the time of Reagan's speech, and no communications links had been set up.
Myth #7: An unavoidable price for progress
Claims that the disaster was the unavoidable price to be paid for pioneering a new frontier were self-serving rationalizations on the part of those responsible for incompetent engineering management — the disaster should have been avoidable. NASA managers made a bad call for the launch decision, and engineers who had qualms about the O-rings were bullied or bamboozled into acquiescence. The skeptics’ argument that launching with record cold temperatures is valid, but it probably was not argued as persuasively as it might have been, in hindsight. If launched on a warmer day, with gentler high-altitude winds, there’s every reason to suppose the flight would have been successful and the troublesome seal design (which already had the attention of designers) would have been modified at a pace that turned out to have been far too leisurely. The disaster need never have happened if managers and workers had clung to known principles of safely operating on the edge of extreme hazards — nothing was learned by the disaster that
, and then forgotten.
NBC News space analyst James Oberg spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer.
Photos: The Challenger tragedy in pictures
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The shuttle Challenger's mission in 1986 was meant to mark a milestone in spaceflight: the first orbital voyage of an American teacher. NASA's choice for the honor was Christa McAuliffe, a social-studies teacher at Concord High School in New Hampshire. Here, McAuliffe rides past the New Hampshire State House in Concord with her daughter Caroline and son Scott, during a Lions Club parade on July 21, 1985.
(Jim Cole / AP)
High-school teacher Christa McAuliffe folds her training uniform as she packs for the trip to Johnson Space Center in Houston on Sept. 8, 1985.
(Jim Cole / AP)
The space shuttle Challenger is transferred to the high bay of the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida on Dec. 17, 1985. Inside the cavernous VAB, the Challenger orbiter was mated with its solid rocket boosters and external tank in preparation for its launch a month later.
(Terry Renna / AP)
Christa McAuliffe gets a preview of microgravity on NASA's specially equipped KC-135 "zero gravity" aircraft on Jan. 13, 1986. The plane flies in a parabolic pattern that provides short periods of weightlessness. For some people, those bouts of zero-G can induce nausea - which is why the airplane was nicknamed the "Vomit Comet."
(Science & Society Picture Library / Getty Images)
The shuttle Challenger is delivered to its launch pad at NASA's Kennedy Space Center atop a mobile crawler-transporter.
Challenger's crew members practice the procedure for escaping from the launch pad at Kennedy Space Center using slide wire baskets. From left are Ronald McNair, Gregory Jarvis and Christa McAuliffe. Directly behind them are astronauts Judy Resnik and Ellison Onizuka. The basket system was designed to take the astronauts off the pad quickly if an emergency arose just before launch.
(NASA Headquarters)
Challenger's crew members stand in the White Room at Launch Pad 39B after a dress rehearsal for launch. From left are Christa McAuliffe, Gregory Jarvis, Judy Resnik, commander Dick Scobee, Ronald McNair, pilot Michael Smith and Ellison Onizuka.
(NASA Headquarters)
Challenger's crew members leave their quarters at Kennedy Space Center for the launch pad on Jan. 27, 1986. Commander Dick Scobee is at the front of the line, followed by Judy Resnick, Ronald McNair, Gregory Jarvis, Ellison Onizuka, Christa McAuliffe and pilot Michael Smith. NASA had to scrub the launch attempt on Jan. 27, due to high winds at the pad, and liftoff was rescheduled for Jan. 28.
(Steve Helber / AP)
A launch-pad camera captures a close-up view of the shuttle Challenger's liftoff on Jan. 28, 1986. From this camera position, a cloud of gray-brown smoke can be seen on the right side of the solid rocket booster, directly across from the letter "U" in "United States" on the orbiter. This was the first visible sign that a breach in the booster's joint may have occurred. Investigators determined that frigid overnight temperatures caused the booster joints' normally pliable rubber O-ring seals to become hard and non-flexible. The failure of the seals caused hot exhaust gases to blow through the joints, cutting into the external fuel tank.
(NASA Headquarters)
Related story
A wide-angle view shows the ascent of the shuttle Challenger on Jan. 28, 1986. In the seconds after ignition, the rocket engines' hot blast began the process of destruction.
(NASA Headquarters)
Why did the O-rings fail? On the day of the shuttle Challenger's launch, icicles draped structures at NASA's Kennedy Space Center in Florida. The unusually cold weather, beyond the tolerances for which the rubber seals were approved, most likely caused the O-ring failure.
(NASA Headquarters)
Classmates of the son of America's first teacher-astronaut cheer as the space shuttle Challenger lifts skyward from Launch Pad 39B on Jan. 28, 1986.
Their delight turned to horror as the shuttle exploded 73 seconds into flight. The boy in the white hat and glasses at center is Peter Billingsley, the star of "A Christmas Story" and a spokesman for the young astronaut program.
(Jim Cole / AP)
The right solid rocket booster on the shuttle Challenger begins to explode, just a little more than a minute into the shuttle's ascent from NASA's Kennedy Space Center on Jan. 28, 1986.
(NASA via AFP-Getty Images)
An orange fireball marks the explosion of the space shuttle Challenger on Jan. 28, 1986.
(Bruce Weaver / AP)
At about 76 seconds, fragments of the orbiter can be seen tumbling against a background of fire, smoke and vaporized propellants from Challenger's external fuel tank. The left solid rocket booster is still shooting skyward. A reddish-brown cloud envelops the disintegrating orbiter. The color is indicative of the nitrogen tetroxide oxidizer propellant in the orbiter's reaction control system.
(NASA Headquarters)
This picture, released by the presidential commission that investigated the Challenger tragedy, shows fragments of the orbiter flying away from the explosion on Jan. 28, 1986, 78 seconds after liftoff. The top arrow shows the orbiter's left wing. The center arrow shows the orbiter' and the bottom arrow shows the orbiter's forward fuselage. Investigators suggested that some of Challenger's crew members may have survived the explosion itself but died in the fall down to Earth.
Flight director Jay Greene studies data at his console inside Johnson Space Center's Mission Control Center in Texas, just minutes after the announcement that Challenger's ascent was not nominal.
Members of teacher-astronaut Christa McAuliffe's family react shortly after the failed liftoff of the space shuttle Challenger from NASA's Kennedy Space Center on Jan. 28, 1986. Christa's sister, Betsy, is in front, with parents Grace and Ed Corrigan behind.
(Jim Cole / AP)
Carina Dolcino, senior class president at Concord High School, is stunned by the news that the space shuttle carrying Christa McAuliffe, one of the school's teachers, exploded after launch on Jan. 28, 1986. Students watched the launch on television sets scattered throughout the school in Concord, N.H., and a celebration had been planned for a successful liftoff.
(Ken Williams / Concord Monitor via AP)
President Ronald Reagan, center, is surrounded by members of his senior staff on Feb. 3, 1986, as he watches a TV replay of the Challenger shuttle explosion at the White House. From left are Larry Speakes, deputy White H presidential assistant Dennis T special assistant Jim K R White House communications director Patrick B and chief of staff Donald Regan.
(Peter Souza / AP)
Lisa Mitten of Concord, N.H., wipes tears from her eyes as her daughter Jessica reads some of the letters of sympathy that were on display at Concord High School on Feb. 1, 1986. Hundreds of Concord residents visited the school library to see the many telegrams and letters that were sent from all over the United States.
(Toby Talbot / AP)
Debris from the ill-fated shuttle Challenger is unloaded from the Coast Guard cutter Dallas during February 1986.
For weeks after the accident, search and recovery teams went out to retrieve Challenger debris from the Atlantic Ocean, with the help of the U.S. Coast Guard and U.S. Navy. Vessels brought pieces of debris to the Trident Basin at Cape Canaveral Air Force Station, from which they were shipped to Kennedy Space Center for investigation. The Coast Guard cutter Dallas transported this fragment of exterior tiling.
(NASA Headquarters)
A piece of debris from the space shuttle Challenger is hoisted onto the deck of the Stena Workhorse off the coast of Florida during a recovery mission.
(Time & Life Pictures via Getty Images)
The remains of the shuttle Challenger's seven crew members are transferred from seven hearses to a MAC C-141 transport plane at the Kennedy Space Center's Shuttle Landing Facility, for transport to Dover Air Force Base, Del.
(NASA Headquarters)
President Ronald Reagan and his wife, Nancy, stand with the wife of astronaut Michael Smith and other family members at a memorial service for the victims of the Challenger disaster.
(Diana Walker / Time & Life Pictures via Getty Image)
Apollo 11 moonwalker Neil Armstrong, a member of the presidential panel investigating the Challenger explosion, listens to testimony before the commission in Washington on Feb. 11, 1986. Another commission member, David Acheson, listens in the background. A model of the space shuttle sits on the table.
(Scott Stewart / AP)
Search and recovery teams located pieces of both the left and right sidewall of the shuttle Challenger during the months-long retrieval effort that followed the explosion on Jan. 28, 1986. Heat and fire damage scarred the right sidewall. But the left sidewall, depicted here, escaped the flames and suffered only from overload fractures and deep gouge marks. The largest intact piece formed part of the payload bay sidewall and measured approximately 30 by 12 feet.
(NASA Headquarters)
Some pieces of the shuttle Challenger did not surface until long after the explosion. A tractor carries one of the shuttle's elevons after it washed ashore on Cocoa Beach, Fla., on Dec. 17, 1996 ... almost 11 years after the loss of Challenger and its crew.
(AFP-Getty Images)
Every January, NASA recalls the Challenger explosion as well as other space tragedies on a "Day of Remembrance." Here, NASA Administrator Sean O'Keefe lays a wreath at the Space Shuttle Challenger Memorial at Arlington National Cemetery in Virginia on Jan. 28, 2003. O'Keefe also paid tribute to the three astronauts of Apollo 1 who died in a launch pad fire on Jan. 27, 1967. Sadly, seven more astronauts died just days after this picture was taken, on Feb. 1, 2003, when the shuttle Columbia broke up during re-entry.
(Bill Ingalls / NASA via Getty Images)
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