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（呼氣） has a tendency to form an invisible（隱的） 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 （生死攸關(guān)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 這是一篇說明文．本文通過舉例說明了太空生活的奇妙：在太空睡覺時，對宇航員來說主要的挑戰(zhàn)在于恰當(dāng)?shù)乃咦藙荩挥詈絾T在一個地方運動久了會出現(xiàn)碳毒性頭痛；宇航員的大腦接收到矛盾的信息時會感到惡心．最后告訴我們美國國家宇航局對宇航員主要的擔(dān)心是宇航員回家后的修養(yǎng)期和如何在太空長久地保持健康．
解答 29．D．細(xì)節(jié)理解題．根據(jù)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"可知宇航員在一個地方運動久了會出現(xiàn)碳毒性頭痛．故選D項．
30．C．細(xì)節(jié)理解題．根據(jù)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．"可知宇航員在大腦接收到矛盾的信息時會感到惡心．故選C項．
31．A．細(xì)節(jié)理解題．根據(jù)最后一段倒數(shù)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…"可知美國國家宇航局對宇航員主要的擔(dān)心之一是如何在太空長久地保持健康．故選A項．
點評 考察學(xué)生的細(xì)節(jié)理解和推理判斷能力，做細(xì)節(jié)理解題時一定要找到文章中的原句，和題干進(jìn)行比較，再做出正確的選擇．在做推理判斷題不要以個人的主觀想象代替文章的事實，要根據(jù)文章事實進(jìn)行合乎邏輯的推理判斷．
