3. What is NOT true about the scramjet engine?
A It goes slower than a rocket.
B It extracts oxygen from the air that flows through the engine.
C It works only at speeds greater than five times the speed of sound.
D It doesn’t carry its own oxygen supply.
4. What did Werner J.A.Dahm of the University of Michigan say about the Hyper-X test flight?
A It indicated the birth of a very fast airplane.
B It was self-powered，so it lasted only 11 seconds.
C It can transportcargo quickly and cheaply to the brink of space.
D It is a major milestone in the journey of making a new type of very fast airplanes，
5. What has NASA planned to do?
A To make another 11-second hypersonic flight at 10 times the speed of the sound.
B To make three more Hyper-X experiments.
C To retest the aircraft that is left.
D To make the aircraft fly higher and longer.
答案与题解：
1. C Hyper-X之所以打破纪录是因为它的飞行速度是音速的7倍。它不是第一架空气喷气式飞机，也不是第一架超音速飞机，所以A和D都不对。Hyper-X的试飞并未绕赤道飞行，所以B也是错误的选择。
2. B 第四段讲了三种发动机的氧气：喷气式发动机是从空气中汲取氧气，火箭发动机必须自携氧气，而超音速冲压喷气发动机则不必白携氧气，而这正是Hyper-X使用的发动机装置。
3. A 根据第五段内容，B、C、D都是正确的说法。第四段最后一句告诉我们，A的说法是不正确的。
4. D 文章的第六段中，密歇根大学的研究人员Werner J.A.Dahm说，Hyper-X的试飞成功只是研制一种新式快速飞机过程中的一个里程碑(a major milestone on the way to a new breed of very fast airplanes)，而不是新型飞机的诞生。所以，D是正确选择，A是错误选择。B也不是Werner J.A.Dahm想要表达的意思。C是其他下程师而不是Werner J.A.Dahm说的话。
5. A 答案可在最后一段找到。