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  3. A greenhouse is a building made of glass which is used for keeping plants warm when the outside temperature is low. In a similar

A greenhouse is a building made of glass which is used for keeping plants warm when the outside temperature is low. In a similar

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问题     A greenhouse is a building made of glass which is used for keeping plants warm when the outside temperature is low. In a similar way there are several gases in the atmosphere which trap the heat produced by the sun and prevent it from escaping. These gases are known as "greenhouse gases", and the way in which they trap heat in the atmosphere is called the "greenhouse effect". This is not simply air pollution. Most of the main greenhouse gases exist naturally in small amounts in our atmosphere, and without them the earth would be 30 degrees colder and human life would not exist. In other words, the greenhouse effect is a natural course which is to some degree helpful to us.
    The problem is that in the last century and a half, we have been putting too many of these gases into the earth’s atmosphere by burning large quantities of coal and oil and by cutting down forests. The rapid increase in the greenhouse gases is making the world warmer. The world’s temperature has already gone up by half a degree this century, and the sea level has risen by 10 centimeters. If the amount of carbon dioxide in the atmosphere doubles there will be a rise in the earth’s temperature of between 1 and 4. This may seem a small increase, but it would be enough to cause major changes in geography and agriculture. Large areas of the world would be flooded, and some areas would become dry and unable to produce crops. It is important, too, to consider that there may be a delay of about 30 years in the greenhouse effect. This means that we are probably experiencing only now the effect of the gases put into the atmosphere before the 1960s. Since then, these gases have greatly increased.
If there was no greenhouse effect,______.
选项 A、no plants would grow on our planet
B、the earth would be thirty degrees colder
C、man could not live on the earth
D、all of the above answers are correct
答案D
解析 根据第一段倒数第三行…without them the earth would be 30 degrees colder andhuman life would not exist．可知没有温室气体，地球上的温度会比现在低30度，而且人类将不复存在。故B和C都正确，A通过推测也正确，D包含了B、C、A三项，故选择D项。
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