We’ve talked about snails (蜗牛) and their slow move. But much of the time snails don’t move at all. They’re in their shells—sleeping.

Hot sun will dry out a snail’s body. So at the least sign (迹象) of hot sun, a snail draws its body into its shell and closes the opening with a thin cover. Then it goes to sleep. A snail will die in a heavy rain. So whenever it rains, it goes to sleep. A snail can sleep for as long as it needs to. It can take a short sleep. Or it can sleep for days at a time. And it spends all the winter months in its shell, asleep.

In Spring the snail wakes up. Its body, about three inches long, comes out from the shell. When hungry, the snail looks for food. It can’t see very well. Its eyes, at the ends of the top feelers (触角), are very weak. But its sense of smell is very strong. So its little mouth goes to work.

A snail’s mouth is no bigger than the point of a pin (针). Yet it has 256,000 teeth! The teeth are so small that you can’t see them. But they do their work. If you put a snail in a hard paper box, it will eat its way out! And if a snail wears out (磨坏) its teeth, it will grow new ones.

Mostly, a snail looks for food at night. It can go on eating for hours and never feel full.

There are many kinds of animals in this world and some of them are our friends. But can animals be made to work for us?

Some scientists think that one day animals may be taught to do some jobs. In films or on TV we have already seen some animals like elephants, monkeys, dogs, bears, or other animals doing a lot of easy things. If you watch carefully, you may find that those animals are always given a little food to eat after they have done something. Scientists say that it is true that many different animals   may be taught to do lots of easy jobs if they know they will get something to eat.

We all know elephants can carry large pieces of wood with their strength, and dogs can look after houses for people. And we also teach animals to work in factories. Apes ( 猿 ), for example, have been used in America to make cars, and scientists believe that these large monkeys may one day get in corn or drive trains. People are training them to do those things.

If you watch the sky for about an hour after the sun goes down, you may see some “moving stars”. But they’re not real stars. They’re man –made satellites (人造卫星). And the biggest of all is the International Space Station (ISS). From May to July is the best season to watch the ISS flying over the earth. And people can see it with their eyes.

The ISS is the biggest satellite and scientists want to live on it. They think that the best way to learn more about space is to live there.

When the space station is finished, it will be like a city in space. People will stay and study there with many of the things they have at home. Laboratories (实验室), living rooms and power stations are being built. The ISS is the most expensive space program. Billions of dollars are being spent on it every year.

Scientists hope that the ISS will be a stepping stone for future space exploration (探测). “The ISS will help us understand the human body better, explore space and study the earth. It can help us make life on the earth better.” said Kathryn Clark, an ISS scientist.

The US, Russia, Canada, Japan, Brazil and 11 European countries are parts of the program. China isn’t an ISS country, but it has helped with some of the experiments. In 2003, China sent some rice up to the ISS to find out what space would do to it.