阅读理解：ThereareplantsinNorthAfricawheregreatcitiesoncestood.Thereweregar

阅读理解：There are plants in North Africa where great cities once stood. There were gardens and trees and grasses. But now these places are like deserts (a large land of sand). Scientists have begun to study this land to find out what happened. Many of them think the land died when the trees were cut down. Trees help other plants grow. Tree roots(根) hold the soil (the top of the earth where plants grow) in place. They keep the soil from blowing away. In forests, leaves on the ground keep rain-water from running off. Trees near farms protect (keep something safe) growing plants from strong winds.Once there were hundreds of farms in the southwest United States. Then the farms turned into fields of dry land. Trees might have saved these farms. But few trees grow in the dry Southwest. Now we try to save trees. In many forests, when a tree is cut down, a new tree is planted in its place. We do not want the land to die.The writer wants to tell us that ________.A.farms are better than citiesB.there are no deserts in AfricaC.trees are important to the landD.trees are quite important to American farms

C解析这篇文章自始至终围绕“树对土地和农业的影响”这一话题展开叙述，通过引用“北非”和“美国西南部”两个典型例子予以左证，并详细讲述了树根、叶是如何防止水土流失，以及森林是如何防止风沙流动，来证实树木对土地的重要性。因此

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