题目内容：

Some trees can survive a long time without watering. Think of trees that grow in the desert. But other trees may need more moisture(水分)than they can get from rainfall or from the air.

The soil stores moisture during cooler weather. But most of that moisture is gone by the middle or rend of the hottest months of the year. Trees and other plants can look thirsty. Leaves can become droopy(下垂的)and hang downward. They can also turn yellow. Yellowing can be a sign of too much water. But it can also be a warning sign of too little water.

With a newly planted tree, the roots not yet spread out from the root ball. The root ball can become dry faster than the dirt around it. So put water on the area of the root ball and the surrounding soil until the roots become established.

Once a tree is well established, water deeply instead of often. The amount of water needed depends on the tree and the soil. Clay soils hold water for longer periods while sandy soils hold less water. During the hottest season, a deep watering may satisfy a tree for anywhere from ten days to four weeks. While watering , we should have a stop, for the soil needs a little time to absorb the water. Otherwise the water runs off the surface and gets wasted. Avoid watering established trees at the base of trunk. This can harm the tree. Too much water in the soil at the base of a tree can lead to the growth of fungi(霉菌). If the area is too wet, harmful organisms have a better chance to invade the tree and cause disease, which is true especially in Mediterranean and semi-dry climates. Many trees in these climates have adapted to having a dry area near their base during the hottest season.

1.What’s the author’s purpose of mentioning desert trees in the first paragraph?

A. To tell the truth that there is life in the desert

B. To prove trees can get water in a natural way

C. To explain how trees collect and store rainfall

D. To show how trees absorb moisture from the air

2.Why shouldn’t an established tree be watered at the base of its trunk?

A. To speed up the absorption of water

B. To reduce the amount of water needed

C. To enable the soil to hold water longer

D. To make it less likely to catch diseases

3.According to the passage, which of the following is TRUE?

A. Most moisture stored by the soil is kept even after hot months

B. Newly planted trees should be watered more deeply than often

C. Trees don’t necessarily lack water when their leaves turn yellow

D. Different soils’ water-holding abilities are more or less the same

4.What is the main idea of the passage?

A. How can trees survive without watering?    B. What makes leaves yellow?

C. How can we water trees?    D. What will harm trees?