1. 完形填空

    We know that trees are useful in our everyday life. They1 us many things, such as wood, oxygen, rubber, medicines and many other things. They can2 tell us a lot about our climate(气候）. The following are reasons. If you3 a tree, you can see that it has many rings(年轮). Most trees grow one new ring4 year. Because of the reason, we know5 a tree is. A tree over a hundred years old means that it has more than a hundred6 When the climate is dry or very cold, the trees do not grow very much and their rings are usually 7 When it is wet and warm, the rings are much thicker. If the rings are suddenly very thin or suddenly very thick, this means that the 8changed suddenly. If we look at the rings on this tree, we can learn about the 9 for a hundred years. We can see10 our climate is changing today.