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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) .
(34)
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A．When there are two lines of plants in each windbreak.B．When there is space left for
Darwin's great work, The Origin of Species, is now generally accepted as one of the most important books ever written. But when it first came out in 1859, it was both derided and bitterly condemned by scientists and laymen.
Much of opposition to The Origin of Species arose from Darwin's claim that all living creatures, including man, are somehow related. Many people were outraged by the suggestion that man shared a common ancestor with animals such as apes and monkeys. They attacked Darwin for saying that man had descended from the apes.
But Darwin never actually said this. He believed that modern men and modern apes have both descended from the same ancestor. But at some time in pre-history, millions of years ago, men and apes began to develop separately, and ever since have continued to take on different characteristics. Today, more than 90 years after Darwin's death, this is the opinion which scientists continue to hold.
In his works, Darwin described the progression of life from its earliest forms. First came the invertebrate-creatures without a backbone. Then invertebrates evolved into fish; fish into amphibians; amphibians into reptiles; and reptiles into birds and mammals.
Fossil remains found after his death show that Darwin was right. Perhaps the most amazing fact about his theory is that he managed to work it out with the aid of only a few fossil discoveries.
Fossil remains were not the only information which we now possess but which Darwin lacked. He did not know that apes have the same diseases as men; nor that they and men have the same kind of blood. Nor did he know about the modern uses of radiation which enable scientists to tell the age of fossil remains and so estimate the speed at which evolution has taken place.
Which of the following best describes the passage as a whole？
A．By creating chances of teamwork.B．By supporting people in war areas.C．By collecting
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【C1】
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