We have all played with snow and ice. When a piece of ice     1     (take) into a warm room, it becomes smaller and smaller, until in the end it disappears completely. Where has it gone? It has been turned into water by the heat.

In winter, when clothes are washed they don’t dry easily. They are often hung up near a fire. Soon steam can be seen     2     (rise) from the wet clothes. The water in them is being turned into vapor(水蒸气), and they get drier and drier. When no more steam comes out, they must be taken away from the heat of the fire,     3     they might get burnt.

If you hold a mirror close in front of your mouth and blow on it, you will find the glass covered at once with little drops of water. The warm water vapor in your breath has been changed into water on the cold glass. Now stop     4     (blow), and soon you will find the glass clear again — the little drops of water has disappeared because they have again been turned into vapor     5     the warm air around them.

    6     (leave) a basin (脸盆) of water outside in freezing weather, and it will soon be covered with ice.     7     it is not taken inside the room, sooner or later the whole basin of water may be turned into a block(块) of ice.

Most matter (物质) has three states(状态): solid(固体), liquid(液体) and gas. Solids can usually be turned into liquids and liquids into gases if we raise their temperature high enough. On the other hand, gases can often be turned into liquids and liquids into solids if they     8     (make) cold enough.

This change of state is a     9     (physics) change and not a chemical one. If a piece of wood is heated to a high temperature, it begins to burn. Light and heat     10     (send) out, together with heavy smoke, and soon only black charcoal(木炭) is left. This is called a chemical change.