单选题

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The 10th launch of the space shuttle Challenger was scheduled as the 25th space shuttle mission. Francis R. (Dick) Scobee was the mission commander. The crew included Christa McAuliffe, a high-school teacher from New Hampshire. The five other crew members were Gregory B. Jarvis, Ronald E. McNair, Ellison S. Onizuka, Judith A. Resnik, and Michael J. Smith.
After several launch delays, NASA officials overruled the concerns of engineers and ordered a liftoff on a cold morning, Jan. 28, 1986. The mission ended in tragedy. Challenger disintegrated into a ball of fire. The accident occurred 73 seconds into flight, at an altitude of 14020 meters and at about twice the speed of sound.
Strictly speaking, Challenger did not explode. Instead, various structural failures caused the spacecraft to break apart. Although Challenger disintegrated almost without warning, the crew may have briefly been aware that something was wrong. The crew cabin tore loose from the rest of the shuttle and soared through the air. It took almost three minutes for the cabin to fall to the Atlantic Ocean, where it smashed on impact, killing the seven crew members.
All shuttle missions were halted while a special commission appointed by President Reagan determined the cause of the accident and what could be done to prevent such disasters from happening again. In June I986, the commission reported that the accident was caused by a failure of O rings in the shuttle's right solid rocket booster. These rubber rings sealed the joint between the two lower segments of the booster. Design flaws in the joint and unusually cold weather during launch caused the O rings to allow hot gases to leak out of the booster through the joint. Flames from within the booster streamed past the failed seal and quickly expanded the small hole. The flaming gases then burned a hole in the shuttle's external fuel tank. The flames also cut away one of the supporting beams that held the booster to the side of the external tank. The booster tore loose and ruptured the tank. The propellants (火箭燃料) from the tank formed a giant fireball as structural failures tore the vehicle apart.
The commission said NASA's decision to launch the shuttle was flawed. Top-level decision makers had not been informed of problems with the joints and O rings or of the possible damaging effects of cold weather.
Shuttle designers made several technical modifications, including an improved O-ring design and the addition of a crew bail-out system. Although such a system would not work in all cases, it could save the lives of shuttle crew members in some situations. Procedural changes included stricter safety reviews and more restrictive launching conditions. The space shuttle resumed flying on Sept.29, 1988, with the launch of the redesigned shuttle Discovery. (465 words)

单选题 The word "overrule" in the first sentence of paragraph 2 means ______.

单选题 The crew died as a direct result of ______.

【正确答案】 A

【答案解析】意为，“机舱落到水面时的冲击力”。第三段指出，严格地讲，“挑战者”号航天飞机并没有爆炸(虽然大家看到了火球)，各种结构上的故障使它解体了，机舱与其他部分分离后落下，用了三分钟左右的时间到达大西洋水面，落向水面的冲力摧毁了机舱，使七名机组人员丧生。这是他们丧生的直接原因。C意为：“航天飞机的解体”。这相对于冲击力来说是间接原因。D意为：“助推器的故障”。根据第四段第二句，问题的确始于宇航飞机右边的火箭助推器上的O形圈。但是，这不是让宇航员丧生的直接原因。

单选题 Investigation by the special commission revealed that ______.

【正确答案】 D

【答案解析】意为：“悲剧至少是由三方面的原因共同作用产生的。”根据第五段，这三方面的主要原因包括：宇航局官员们的错误决定(另见第二段第一句)，O形圈技术故障(另见第四段)，以及寒冷的天气(另见第四段)。A意为：“宇航局上层官员武断的起飞决定。”见第二段第一句。B意为：“宇航飞机的设计者没有检测到助推器的毛病。”C意为：“寒冷的天气使O形圈脱离了火箭助推器。”根据第四段，出问题的O形橡胶圈的作用是密封助推器下两级的接口，由于接口的设计问题和异常寒冷的天气，热气体从接口处透过橡胶圈漏出助推器，助推器中的火苗穿过密封圈并使穿孔扩大，火苗又将宇航飞机的外层燃料箱烧穿，进而将连接助推器和外层燃料箱的一个支柱切断，结果，助推器脱离机体并撕裂了燃料箱，造成了飞机解体，燃料起火。A、C表达的内容均不全面，只表达了部分原因。

单选题 It is obvious from Paragraph 4 that the chief cause leading to the disaster is ______.

单选题 Which of the following is mentioned as an improvement on the launch of Discovery?

【正确答案】 D

【答案解析】根据最后一段，宇航飞机的设计者做了几方面的技术改进，包括改进了O形圈的设计，增加了跳伞 (bail-out)系统，虽然跳伞系统不可能是万能的，但在某些情况下却可以拯救宇航员的性命。程序上也做出了改进，包括更严格的安全检查，更严格的升空条件。根据上下文，这里所说的launching conditions包括天气情况。1988年9月29日，改进后的航天飞机(“发现者”号)成功升空。从以上分析来看，改进内容不包括A、B、C所提到的内容。