9．
完形填空
We
know that trees are useful in our1life. They give us wood,
oxygen, rubber, medicine and many other things. They can2tell
us about our climate (气候). If you3a
tree trunk, you can see that it has many rings (年轮).
Most trees grow one new ring every year. Because of this reason, we know the4of
a tree. A tree over a hundred years old means that it has more than a hundred
rings. When the climate is dry or very cold, the trees do not grow very much
and their rings are usually5. 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 climate changed suddenly. We can learn about the climate for a
hundred years. We can see6our climate is changing today.
