C.Seeking a way to fall asleep quickly

D.Finding a right time to go to sleep.

2.The astronauts will suffer from a carbon-dioxide headache when _____.

A.they circle around on their bikes

B.they use microcomputers without a stop

C.they exercise in one place for a long time

D.they watch a movie while pedaling

3.Some astronauts feel sick on the station during the first few days because _____.

A.their senses stop working

B.they have to stand up straight

C.they float out of their seats unexpectedly

D.whether they are able to go back to the station

4.One of the NASA's major concerns about astronauts is _____.

A. how much exercise they do on the station

B.how they can remain healthy for long in space

C.whether they can recover after returning home

D.whether they are able to go back to the station

【答案及解析】：

答案：1.A; 2.C; 3.D; 4.B

解析：1.这是一篇说明文。本文通过举例说明了太空生活的奇妙:在太空睡觉时,对宇航员来说主要的挑战在于恰当的睡眠姿势;宇航员在一个地方运动久了会出现碳毒性头痛;宇航员的大脑接收到矛盾的信息时会感到恶心。最后告诉我们美国国家宇航局对宇航员主要的担心是宇航员回家后的修养期和如何在太空长久地保持健康。

细节理解题。根据第二段第一、二句"First consider something as simple as sleep. Its position presents its own challenges."可知在太空睡觉时,对宇航员来说主要的挑战在于恰当的睡眠姿势。故选A项。

2.细节理解题。根据第三段中"But station residents have to be careful about staying in one place too long. ...You can end up with what astronauts call a carbon-dioxide headache"可知宇航员在一个地方运动久了会出现碳毒性头痛。故选C项。

3.细节理解题。根据第四段中"Your inner ear thinks you're failing. Meanwhile your eyes are