Daily exercise is essential. The lack of gravity makes bones more fragile and muscles lose strength - so astronauts are encouraged to work out for at least two hours a day.

　　The role of astronauts in the International Space Station is to act as lab technicians for scientists back on earth. So they spend their time maintaining their environment and performing and monitoring experiments in a confined space about the size of a Boeing 747. Almost every task is carefully planned by mission control - although most astronauts spend their first days losing things until they get used to sticking everything they use to the walls with Velcro, duct tape (强力胶带) or clips (夹子)．

　　One of their most valued perks (额外待遇) is the view from "the office"， dominated by that gigantic blue ball down there, sitting in the darkness of space. Wow! Absolutely breathtaking!

　　1．When they sleep upside down, the astronauts will not get dizzy because ________.

　　A．they don't feel it

　　B．they sleep in the daytime

　　C．they sleep in special sleeping bags

　　D．they are trained to adapt to the conditions of weightlessness

　　解析：选A　细节理解题。根据第二段的"American astronaut Sunita Williams explains, 'It's like a little phone booth, but it's pretty comfortable and it doesn't matter if I turn over and sleep upside down. I don't have any sensation (感觉) in my head that tells me I'm upside down.'"可知，宇航员倒着睡不会晕是因为大脑并没有感知到这种颠倒的行为，故选A。

　　2．Why may astronauts lose things?

　　A．Because they always forget where they put their things.

　　B．Because in zero gravity, everything that is not stuck down floats.

　　C．Because they are so busy that they don't have enough time to put their things away.

　　D．Because in a space station, there aren't enough places for astronauts to store their things.

　　解析：选B　推理判断题。根据第二段的第二句"They spend the night floating in a sleeping bag inside a small cubicle (小隔间) on the ceiling"和第三段的第二句"Can you imagine the mess that running water would make in zero gravity"以及第五段的最后一句"Almost every task is carefully planned by mission control - although most astronauts spend their first days losing things until they get used to sticking everything they use to the walls with Velcro, duct tape (强力胶带) or clips (夹子)"可知，在失重状态下没有被固定的东西会飘浮起来以至于会丢失，故选B。

　　3．What parts become weak if astronauts don't exercise?

A．Their teeth and bones.