根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。
Can you imagine astronauts' everyday life in space? They also need to eat, 1 , exercise and relax. They do the same things as us, but they do2 differently.
On Earth, we put food on a plate and water in a glass. Gravity(重力) holds the food down and keeps the water in the glass. 3 there is almost no gravity in space, so food can float(漂浮) away, and astronauts must eat and drink4 .
Sleeping is very different in space. Some astronauts like to float in the air, but most like to be in a 5bag. They tie the bag to a wall 6 they won't float away at night. Exercise is very important in space. On Earth, your legs 7 your body, but in space, astronauts float. So they do not use their legs often. This is very 8their 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 9 the radio. Sometimes they just enjoy 10 in the air.
组织发挥作用受诸多因素制约