56. As we know, we put food on a plate and water in a glass on earth. Gravity(引力) holds the food down and keeps the water in the glass. But in space, there is almost no gravity. So food can float away, and astronauts must eat and drink carefully.

57. in space, sleeping is very different. Some astronauts like to float in the air, but some astronauts like to be in a sleeping bag. They tie the bag to a wall so that they can’t float at night.

58. 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. This is bad for their legs, or they exercise for   thirty minutes every day. They often use an exercise bike for this.

59 Many people can use computers, but few of them know how to look after them. Remember the following when you use computers: Keep your computer in a cool, dry room; do not put water or food near your computer; keep you screen clean and not too bright.

60. Some things can carry messages. For example, a sing at the bus stop helps you to know which bus to take. Sings on the door tell you where to go in or out. Have you ever noticed that there are a lot of signs around you and they you receive messages form them all the time?