—Sorry, Mum. I'll _________it off at once.

—OK, Murn Please_________ me up earlier tomorrow morning.

—Certainly.

    Water is the1of all the things we eat and drink. Not many people understand this but2quite true. The human body3go without food for a long time. We've got many examples for this. Yet two4three days without water can usually make people5. Man can't live6water.

    Many people don't understand how7water the human body needs8work well, and many people, especially young people, do not drink enough,9in very hot weather. Our body is mostly water, about 65% to 75%. That is to say about two thirds of our body is water. When we do sports, some of the water will get away from our body.10we don't drink some water, we won't have enough water. If we don't have enough water, we'll feel tired and many of us will get ill. So you know how important water is to us.

    Many years ago, most of our earth was covered with blocks (块) of ice. These ice blocks were as tall as high buildings in modern cities. Most of the ice was in the northern part of the world. Then the ice blocks started to move south. Cold and rain came with the ice. Animals had to move. At last, the ice began to melt (融化). After half a million years, most of it melted. More than half of the earth became covered with water. The climate became much warmer. Things began to grow. The earth began to look the way in which it looks today.

Wow, you have books I have!