we know that trees are useful in our everday life.they ( give ) us many things,such as wood,oxygen,rubber,medicines and many other things.they can（ also ）tell us a lot about our climate.the following are the reasons.if you( cut )a tree ,you can see that ir has many rings.most trees gro one new ring( each/every ) year.because of this reason,we know( 这句话有问题,在查查原文 )a tree is.a tree over a hundred years old means that it has more than a hun dred( rings ).when the climate ids dry or very cold,the trees do not grow very much and their tings are usually( thin/narrow ).when it is wet and warm,the rings are much thicker.if the tings are suddenly very thin or suddenly very thick,this means that the ( weather )changed suddenly.if we look at the rings on this tree ,we can learn about the( weather )for a hundred years.we can see( how )our climate is changing today.