3．The fantastic life in space never quite goes away．Here are some examples．
First consider something as simple as sleep．Its position presents its own challenges．The main question is whether you want your arms inside or outside the sleeping bag．If you leave your arms out，they float free in zero gravity，often giving a sleeping astronaut the look of a funny ballet dancer．"I'm an inside guy．"Mike Hopkins says，who returned from a six-month tour on the International Space Station．"I like to be wrapped up．"
On the station，the ordinary becomes strange．The exercise bike for the American astronauts has no handlebars．It also has no seat．With no gravity，it's just as easy to pedal violently．You can watch a movie while you pedal by floating a microcomputer anywhere you want．But station people have to be careful about staying in one place too long．Without gravity to help mix air，the carbon dioxide you exhale（呼气） has a tendency to form an invisible（隐的） cloud around your head．You can end up with what astronauts call a carbon-dioxide headache．
Leroy Chiao，54，an American retired astronaut after four flights，describes what happens even before you float out of your seat．"Your inner ear thinks you're falling．Meanwhile your eyes are telling you you're standing straight．That can be annoying，that's why some people feel sick．"Within a couple of days，truly terrible days for some astronauts'brains learn to pay no attention to the panicky signals from the inner ear，and space sickness disappears．
Space travel can be so delightful but at the same time invisibly dangerous．For instance，astronauts lose bone mass．That's why exercise is considered so vital （生死攸关的） that National Aeronautics and Space Administration （NASA） puts it right on the workday schedule．The focus on fitness is as much about science and the future as it is about keeping any individual astronaut healthy．NASA is worried about two things：recovery time once astronauts return home，and，more importantly，how to keep strength and fitness for the two and a half years or more that it would take to make a round-trip to Mars．
29．The astronauts will suffer from a carbon-dioxide headache whenD
A．they circle around on their bikes．
B．they watch a movie while pedaling．
C．they use microcomputers without a stop．
D．they exercise in one place for a long time．
30．Some astronauts feel sick on the station during the first few days becauseC
A．their senses stop working．
B．they have to stand up straight．
C．their brains receive differing messages．
D．they float out of their seats unexpectedly．
31．One of NASA's mainly considers about astronauts isA
A．how they can remain healthy for long in space．
B．how much exercise they do on the station．
C．whether they can recover after returning home．
D．whether they are able to go back to the station．
分析 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．
解答 29．D．细节理解题．根据第三段中"But station residents have to be careful about staying in one placetoo 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D项．
30．C．细节理解题．根据第四段中"Your inner ear thinks you're failing．Meanwhile your eyes are telling you you're standing straight．That can be annoying-that's why some people feel sick．"可知宇航员在大脑接收到矛盾的信息时会感到恶心．故选C项．
31．A．细节理解题．根据最后一段倒数第一、二句"The focus on fitness is as much about science and thefuture as is about keeping any individual astronaut healthy…NASA is worried about two things：…and，more importantly，how maintain strength and fitness…"可知美国国家宇航局对宇航员主要的担心之一是如何在太空长久地保持健康．故选A项．
点评 考察学生的细节理解和推理判断能力，做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确的选择．在做推理判断题不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
