【正确答案】 D

【答案解析】[听力原文]
Windbreaks are barriers formed by trees and other plants. Farmers plant these barriers around their fields to protect their land.
Windbreaks stop the wind from blowing soil away (33) . They also keep the wind from destroying or damaging crops. They are very important for protecting grain crops.
There have been studies done on windbreaks in parts of West Africa, for example. These found that grain harvests can be twenty percent higher in fields protected by windbreaks compared to fields without such protection (33) .
But windbreaks seem to work best when they allow some winds to pass through them (341. If the wall of trees and plants blocks the wind completely, then violent air motions will take place close to the ground. These motions will lift soil into the air where it will be blown away.
There should be at least two lines in each windbreak. one line should be large treas. The second line, right next to it, can be shorter trees and other plants with leaves. Locally grown trees and plants are best for windbreaks.
If the quality of the land is not very good, studies have shown that one kind of tree that can grow well is the white pine (35) .
Windbreaks not only protect land and crops from the wind. Surplus trees can be cut down and used to provide wood (33) .
33．Which is not an advantage of windbreaks?
题目问哪一项不是防风林的优点。短文中提到了防风林的种种优点，惟独没有提到防风林可以使庄稼避免阳光直射。

【正确答案】 B

【答案解析】[听力原文]
When do windbreaks work best according to the passage?
题目问防风林什么时候效果最好。短文中提到"But windbreaks seem to work best when they allow some winds to pass through them"，可见好的防风林应该留出部分空间让一些风穿过。

【正确答案】 A

【答案解析】[听力原文]
What can we learn from the passage about the white pine?
题目问从短文中对于白松有何了解。短文中提到"If the quality of the land is not very good，studies have shown that one kind of tree that can grow well is the white pine"，由此可以判断A) 正确。