1. Exercise makes your body h      and s         .

2. For strong m      , you need exercise.

3. Sixty m       make an hour.

4. I'm going to w       more sports on TV.

5. You should do more s       for exercise.

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.

1.What does the underlined word "gravity" mean in Chinese?

2.Why do astronauts tie the sleeping bag to a wall?

3.What's the main idea of the passage?