There are three different kinds of matter. They are solids, liquids and gases. 物质分三种：固体、液体和气体。

　　Gas has no shape, so you can't touch gas. 气体本无形，所以你触摸不到。

　　Gas moves very freely. 气体能非常自由地运动。

　　Gas can change into a solid or a liquid when the temperature gets too low. 当温度变得很低时，气体就能变成固体或液体。

　　On the other hand, a solid can change into gas when the temperature gets too high. 反之，当温度变得很高时，固体或液体就能变成气体。

　　Is there a good example of these changes? 有没有这些变化的好例子？

　　Of course, it is dry ice. 当然有，它就是干冰。