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第一节：阅读理解 阅读下面短文，从短文后所给各项的四个选项中，选出最佳选项。
A
How much rain has fallen on the earth in the past? Man has not always kept weather records（记录）. Because scientists need a way to learn about past rainfall（降雨）, they study the tree rings.
A tree’s trunk（树干）keeps growing year by year. Under its bark（树皮）,a tree adds a layer of new wood each year it lives. If you look at a tree stump, you can see the layers. They are called annual ring（年轮）.
On some trees, all of the rings are of the same width. But the ponderosa（美国黄松）that grow in the American southwest have rings in different widths. The soil in the southwest is dry. The pines depend on rainfall for water. In a year of good rainfall, they form wide rings. In a dry year they form narrow ones.
Scientists do not have to cut down a pine to study its rings. With a special tool, they remove a narrow piece of wood from the trunk without harming the tree. Then they look at the width of each ring to see how much rain fell in the year it formed.
Some pines are hundreds of years old and have hundreds of rings. These rings are from an annual record of past rain fall in the southwest.
1. A tree grows a new layer of wood .
A. each week B. whenever it rains C. every year D. every season
2.On the whole, the passage is about .
A. why the tree trunks grow bigger B. why scientists study tree rings
C. trees that lived hundreds of years ago D. the ponderosa in the US
3. The scientists to know how much rain fell in a certain area in the past.
A. climbed up the trees. B. moved the pine tree
C. removed a piece of wood D. studied the width of the tree rings
4. Which of the following does the passage lend you to believe?
A. Young trees have fewer annual rings than old ones. B. The trunk of a tree never changed in size.
C. Trees in the southwest do not need rain. D. The soil in the southwest is fit for the growth of trees.
B
In future a machine&nb
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