2. 外语
  3. All over the world, forests are safeguarding the health of the planet itself. They do this【C1】______protecting the soil, providi

All over the world, forests are safeguarding the health of the planet itself. They do this【C1】______protecting the soil, providi

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问题    All over the world, forests are safeguarding the health of the planet itself. They do this【C1】______protecting the soil, providing water and【C2】______the climate. Trees【C3】______soil to mountainsides. Hills【C4】______the trees have been felled lose 500 times as【C5】______soil a year as those with trees.
   Trees catch and【C6】______rainwater. Their leaves break the impact【C7】______the rains, robbing them of【C8】______destructive power. The roots of trees allow the water to go into the soil,【C9】______gradually releases it to flow down rivers and refill ground-water reserves. Where there are no【C10】______, the rains run in sheets of water off the land,【C11】______the soil with there Land【C12】______with trees and other plants【C13】______20 times more rainwater than【C14】______earth. As they grow, trees absorb carbon dioxide, the main【C15】______of the "greenhouse effect", which【C16】______irreversibly to change the world’s climate. Together, the world’s trees, plants and soils contain three times as much carbon as【C17】______is in the atmosphere.
   The world’s forests【C18】______the vast majority of its animal and plant species. The tropical rainforests【C19】______have well over half of them,【C20】______they cover only about 6% of the Earth’s land surface.
【C15】
选项 A、reason
B、effect
C、purpose
D、cause
答案D
解析 考查名词词义。reason(逻辑上的)原因；effect效应，作用；purpose目的，意图；cause(坏事的)起因，原因。由上下文可知这里指导致出现温室效应的起因是二氧化碳，故选[D] 。
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