Question

阅读下列短文, 从所给的四个选项中, 选出最佳答案。

　　     How much rain has fallen on the earth in the past? Man has not always kept weather records. Because scientists need a way to learn about past rainfall, they study tree rings.

　　     A tree's trunk grows bigger each year. Beneath its bark (树皮), a tree adds a layer of new wood each year it lives. If you look at a tree stump (桩), you can see the layers. They are called annual rings (年轮).

　　     On some trees all of the rings are the same width. But the ponderosa pines that grow in the American southwest have rings of different width. 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 know its rings. With a special tool, they can 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 form an annual record of past rainfall in the southwest. 　　

1. The passage mainly tells us about ___________.

[　　]

A. why tree trunks grow bigger 　　

B. how trees grow　　　　

C. why and how scientists study tree rings 　　

D. how tree rings are formed　　

2. From the passage we can see that ___________.

[　　]

A. a tree grows faster when it has a lot of water 　　

B. scientists cut down trees to study tree rings 　　

C. pine trees form wide rings every year 　　

D. the ponderosa pine only grows in the American southwest

3. A new layer of wood grows in a tree ____________.

[　　]

A. each week　　

B. whenever it rains　　　　

C. every year　　

D. every season　　

4. Why does a ponderosa pine in the American southwest have rings

　　 of different width? ____________

[　　]

A. Because rainfall differs from year to year.

B. The bigger a pine grows, the wider rings it forms.

C. Scientists control its growth.

D. It grows in the dry soil.　　

5. Which of the following is true?

[　　]

A. The trunk of a tree never changes in size. 　　

B. Young trees have fewer annual rings. 　　

C. The soil in the southwest is fit for the growth of trees. 　　

D. It is with a special tool that scientists cut down a tree &

Answer 1

答案：C;A;C;A;B