Can you imagine astronauts' everyday life in space? They also need to eat,  sleep, exercise and relax. They do the same things as us, but they do them differently.
On Earth, we put food on a plate. Gravity holds the food down and keeps it on a place. But there is almost no gravity in space, so food can float （漂浮）away, and astronauts must eat carefully.
Sleeping is very different in space. Some astronauts like to float in the air, but most like to be in a sleeping bag. They tie the bag to a wall so that they won't float away at night.
Exercise is very important in space. On Earth,  your legs carry your body,  but in space, astronauts float, so they do not use their legs often. This is very bad for their legs, so they must exercise for thirty minutes every day.
After a day's work, astronauts relax. They may listen to music, read, watch films, play games, or talk to their friends and families on the radio. Sometimes they just enjoy floating in the air.
【小题1】What does the underlined word "gravity" mean in Chinese?

A: What can I do for you?
B:  1  
A: For your daughter ?Look , the shoes are really nice . Do you like them ？
B: Yes . But I’m afraid my daughter doesn’t like the color . ___2______
A: Sure . There are different kinds of shoes over there . What color does she like ?
B: __3_____And black is her favorite .
A: What size does she need?
B: Size 9. Let me see . Um ,this pair of shoes must fit her ._4______
A: They are not expensive ,only 199 yuan .
B: That would be fine .___5______ Here is the money .Thanks very much.
A: You’re welcome.

----Must he finish the work before supper?

----No, he        . He         finish it after supper.

A．mustn’t; may                         B．needn’t ; can

C．need; can                             D．must; may