We know that trees are useful in our everyday life
They 86 us many things, such as wood, oxygen, rubber, medicines and many other things
They can 87 tell us a lot about our climate(气候)
The following are the reasons(理由)
If you 88 a tree, you can see that it has many rings(年轮)
Most trees grow one new ring 89 year
Because of this reason, we know 90 a tree is
A tree over a hundred years old means that it has more than a hundred 91
When the climate is dry or very cold, the trees do not grow very much and their rings are usually 92
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 93 changed suddenly
If we look at the rings on this tree, we can learn about the 94 for a hundred years
We can see 95 ou