When we talk about the universe, we mean not only the earth, the sun and the moon, but also the stars and space between them. There are millions of stars in our sky. The sun is one of them. Around it there are eight big planets moving, including the earth. The moon is our nearest neighbor in space. If you look at the sky on a clear night, it is possible to see about 3, 000 stars. They look small, but they are really very big hot balls of burning（燃烧着的）gas. Some of them arc huge（巨大的）, but others are much smaller like our planet Earth. The biggest stars are very bright, but they can only live for a short time. Every day new stars are born and old stars die.

    All the stars are very far away. The light from the nearest star（except the sun）takes more than four years to reach the earth.

    Hundreds of years ago, people used stars, like the North Star, to know which direction（方向）to travel in.

Today you can still see that star.

    Can you imagine a pair of shoes that could tie themselves? All you have to do is put them on and push a button. Well, this idea is becoming a reality. The shoe company Nike created the self-tying shoe! This idea first came from the film Back to the Future II, Nike has been working for years to create a shoe that can do this in real life. They have finally done it with Nike HyperAdapt 1.0.

    So how does it work? According to Nike, the shoe is “powered by an underfoot-lacing mechanism(脚下系带装置) small motor that has the power to lace the shoes, All you have to do is put them on, and at first, the shoes are very loose(松的). But then you can push the "+" perfect fit for you. To take them off, all you have to do is push the "-" button, and the shoes will be easily off.

    They haven't been widely released to the public yet, and the price of the shoes is quite high.

    We all know that many inventions have changed our life a lot. They play important roles in our daily life. Here are some interesting inventions.

    Scientists think that there has been life on earth for millions of years. However, we haven't found life on other planets yet. The earth is a planet and it goes around the sun. And there are seven other planets that also go around the sun. The sun and its planets are called the solar system. The solar system is a small part of the universe.

    Scientists have launched many spaceships to explore other planets in the solar system. Some spaceships have gone beyond the solar system. However, no one has discovered any life in space yet.

    Why has no one from other planets sent us a message? Have they tried to send information to us? With so many stars in space, are we alone, or is there life on other planets in space?

    Many people have the wrong ideas about pigs. Pigs are actually(买际上) very clean animals. On farms, they live in dirty places, so they become very dirty. But in the wild, pigs keep themselves very clean.

    They are also very smart. They may he smarter than clogs. So pigs can learn things from people.

    Pigs are very friendly animals. Some people raise (饲养) them as pets. Of course, people raise the smart kind, not the big kind. Small pigs are very cute. And they don't break things in the house. Big pigs usually live outside on the farms, not in people's houses.