A
The oddness of 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 (芭蕾) 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 residents have to be careful about staying in one place too long.Without gravity to help circulate air, the carbon dioxide you exhale (呼气) has a tendency to form an invisible (隐形的) 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 ignore 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 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 maintain strength and fitness for the two and a half years or more that it would take to make a roundtrip to Mars.
文章大意：本文是一篇说明文，从不同角度介绍了在太空中生活时所面对的各种挑战。
21．What is the major challenge to astronauts when they sleep in space？__A__
A．Deciding on a proper sleep position.
B．Choosing a comfortable sleeping bag.
C．Seeking a way to fall asleep quickly.
D．Finding a right time to go to sleep.
解析：细节理解题。第二段谈到宇航员在太空的睡眠，说睡姿是一个很大的问题(Its position presents its own challenges.)，然后以胳膊是否应该放在睡袋里为例解释说明。由此可知宇航员在太空中睡觉时面临的最大问题是睡姿的问题。
22．The astronauts will suffer from a carbon-dioxide headache when __C__.
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
解析：细节理解题；第三段讲到宇航员面临的另外一个问题就是在锻炼的时候，由于没有重力帮助循环空气，宇航员呼出的二氧化碳有可能在头顶形成隐形的云朵，此时宇航员就会出现二氧化碳状态下的头疼，因此选C。
23．One of NASA’s major concerns about astronauts is __B__.
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
解析：细节理解题。最后一段讲到美国国家航空航天局(NASA)关心宇航员的身体健康，他们关心宇航员回到家里之后的恢复期，更重要的是，如何让宇航员在进行火星探测的两年半或更长时间内保持身体健康，这与B项描述是一致的。
