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阅读下面的短文。每篇短文的后面有五个问题，每个问题有四个备选答案。请根据短文的内容选择最佳答案。每个试题计3分,共计15分。 A little airplane has given new meaning to the term going hyper. The Hyper-X is an unmanned，experimental aircraft just 12 feet long. It achieves hypersonic speed using a special sort of engine known as a scramjet3.It may sound like something from a comic book，but engineers have been experimenting with scramjets since the 1960s. Out of the three experimental Hyper-X aircrafts built for NASA5，only one is now left.The agency has plans for another 11-second hypersonic flight，this time at 10 times the speed of the sound. hypersonicadj.超音速的 boostern.助推器 unmannedadj.无人的 booster rocket 助推火箭5skrAmdVet5kB:^Eup 喷气发动机 练习： A it was the first air-breathing jet plane. C it flew at speeds smaller than five times the speed of sound. 2. What kind of an engine did the Hyper-X use? B A scramjet engine that doesnt carry its own oxygen supply. D A iet engine that uses no oxygen. A It goes slower than a rocket. C It works only at speeds greater than five times the speed of sound. | 
