单选题 Climatic conditions are delicately adjusted to the composition of the Earth's atmosphere. If there were a change in the atmosphere--for example, in the relative proportions of atmospheric gases"-the climate would probably change also. A slight increase in water vapor, for instance, would increase the heat-retaining capacity of the atmosphere and would lead to a rise in global temperatures. In contrast, a large increase in water vapor would increase the thickness and extent of the cloud layer, reducing the amount of solar energy reaching the Earth's surface.
The level of carbon dioxide in the atmosphere has an important effect on climatic change. Most of the Earth's incoming energy is short-wavelength radiation, which tends to pass through atmospheric carbon dioxide easily. The Earth, however, reradiates much of the received energy as long-wavelength radiation, which carbon dioxide absorbs and then remits toward the Earth. This phenomenon, known as the greenhouse effect, can result in an increase in the surface temperature of a planet. An extreme example of the effect is shown by Venus, a planet covered by heavy clouds composed mostly of carbon dioxide, whose surface temperatures have been measured at 43012. If the carbon dioxide content of the atmosphere is reduced, the temperature falls. According to one respectable theory, if the atmospheric carbon dioxide concentration were halved, the Earth would become completely covered with ice. Another equally respectable theory, however, states that a halving of the carbon dioxide concentration would lead only to reduction in global temperatures of 312.
If, because of an increase in forest fires or volcanic activity, the carbon dioxide content of the atmosphere increased, a warmer climate would be produced. Plant growth, which relies on both the warmth and the availability of carbon dioxide, would probably increase. As a consequence, plants would use more and more carbon dioxide. Eventually carbon dioxide levels would diminish and the climate, in turn, would become cooler. With reduced temperatures many plants would die; carbon dioxide would thereby be returned to the atmosphere and gradually the temperature would rise again. Thus, if this process occurred, there might be a long-term oscillation in the amount of carbon dioxide present in the atmosphere, with regular temperature increases and decreases of a set magnitude.
Some climatologists argue that the burning of fossil fuels has raised the level of carbon dioxide in the atmosphere and has caused a global temperature increase of at least 1 C. But a supposed global temperature rise of 112 may in reality be only several regional temperature increases, restricted to areas where there are many meteorological stations and mused simply by shifts in the pattern of atmospheric circulation. Other areas, for example, the Southern Hemisphere Oceanic Zone, may be experiencing an equivalent temperature decrease that is unrecognized because of the shortage of meteorological recording stations.

单选题 Which of the following questions does the passage supply information for answering?
【正确答案】 D
【答案解析】推断题。
题意为：“本篇提供信息要回答下列哪个问题?”通读全文；可知作者论述的是有关二氧化碳数量的变化起因及其对大气温度的影响。因此，选项D“大气中二氧化碳含量的常规增减是由什么造成的?”为正确答案。选项A“为何水蒸气水平的变化精确反映出气候的影响?”；选项B“当二氧化碳吸收长波辐射的过程时有哪几个步骤?”；选项C“减少化石燃料的燃烧会对理解温室效有怎样的帮助?”。
单选题 The author is primarily concerned with______.
【正确答案】 C
【答案解析】推断题。
题意为：“作者主要关注______。”在文章第二段，作者论述了大气中二氧化碳含量的变化对全球气温的影响，并列举金星的例子。第三段讲述了燃烧煤、石油等化石燃料造成二氧化碳含量的变化对气温的影响。故选项C“讨论在大气中二氧化碳含量的变化对气候的影响”为正确答案。选项A<‘解释燃烧化石燃料对气候可能造成的影响”；选项B“说明二氧化碳对大气辐射的影响”；选项D“对水蒸气和二氧化碳影响气候的假设提出挑战”。
单选题 The passage suggests that a large decrease in the amount of carbon dioxide in the atmosphere would result in______.
【正确答案】 A
【答案解析】推断题。
题意为：“据文章暗示大气中二氧化碳的含量大幅度降低会导致______。”文中提到如果大气中二氧化碳的含量大幅度增加，温度就会稍微地升高；反之气温下降，故选项A“至少全球气温稍微下降”为正确答案。选项B“至多到达地球的短波辐射稍稍增强”；选项C“全球气温长期少量升高”；选项D“火山活动量长期大量增长”。
单选题 The passage suggests that if there were a slight global warming at the present time, it would be______.
【正确答案】 C
【答案解析】推断题。
题意为：“文中暗示如果目前全球稍微变暖，那么______。”根据第四段第二句 (但是假设实际上全球气温上涨1℃，可能仅仅意味着几个有许多气象站的地区因气流循环模式的变化导致的气温的升高。)，可知C“很难证明气候变暖是燃烧化石燃料造成的”为正确答案。选项A“由于各地大气中二氧化碳含量不同，所以很难测出大气中二氧化碳的增加量”；选项B“很容易显示变暖对大气中水蒸气的影响”；选项D“很容易证明是由云层变厚造成的”。
单选题 All of the following can be found in the author's discussion of climate except______.
【正确答案】 C
【答案解析】细节题。
题意为：“在作者关于气候的讨论中，不包括______。”选项A“关于大气中水蒸气的增加的影响的论述”一段就提到过。选项B“关于大气中二氧化碳含量降低造成影响的两种理论之间的对比”，在第二段提到过。选项D“关于大气中的气体和气候变化之间关系的假设”，末段提到过。故选项C“气象站的效率的概括”为正确答案。