Passage 15                                                     看点评

A green house 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 with out 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 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 probably 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, our use of these gases has greatly increased.

点评

    作好本文的理解测试题的关键是：摈弃先入为主的概念，认真阅读原文。

    本文讨论的“温室效应”问题是目前环保热点问题，妇孺皆知，“温室效应”已是大气污染的代名词，“温室效应”等于空气污染，这是普罗大众已经接受的概念和已经认可的说法。

    但本作者从科学的角度准确地解释了“温室效应”这一概念，为其“正了身”，“平了反”。在第一段里，作者解释了“温室气体”和“温室效应”之后，明确说到：

This is not simply air pollution.  Most of the main greenhouse gases exist naturally in  small amounts in our atmosphere, and with out 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.

    可见“温室效应”是大气层生来具有的一种作用。正由于这种作用，地球上才能万物生长。至于大气污染，全球变暖，则是由于人类活动改变了“温室效应”的过程和作用所至。正如作者所说：

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 greenhouse gases is making the world warmer.

    准确理解温室效应的概念后，我们就不难作对有关中心主旨的三道题了：
题1的答案是B, "Greenhouse effect" means  B. a natural course which is to some degree helpful to us.
题2的答案是D。
题5的答案是C,  The passage mainly deals with  C. the concept and change of greenhouse effect.

    在我们阅读时，有时需要运用我们已有的背景知识来帮助理解。但同时我们也要警惕先入为主的观念干扰影响我们对文章的准确理解。总之，“虚心拜读”，“决不想当然”，才能有有效的阅读。　　      Main Idea