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He goes to work every day ______.

A．except for rainy days                    B．besides it rains

C．but that it rains                         D．except on rainy days

________ there, the southwest desert contains a remarkable variety of plants.

    A. Rarely as it rains                     B. Sometimes it rains

    C. It rarely rains                        D. Although rarely rains

He usually goes to work on time ＿＿＿＿＿＿.

A. except for raining days     B. besides it rains

C. but that it rains     D. except on rainy days

________ is of no concern to us.

A．It rain or not                           B．If or not it rains

C．Whether it rains or not                   D．Will it rain or not

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 the tree rings.

A tree’s trunk (樹干) keeps growing year by year. Under its bark (樹皮), 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 (年輪).

On some trees, all of the rings are of the same width. But the ponderosa(美國黃松) that grows in the American southwest have rings in different withes. The soil in he 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 o0f past rainfall in the southwest.

1.We could infer from the passage that ______.

2.A tree grows a new layer of wood _____.

3.On the whole, the passage is about _____.

4.The scientists _____ to know how much rain fell in a certain area in the past.

5.Which of he following is true according to the passage?