Passage Two

　　Questions 26 to 30 are based on the following passage:

　　In the atmosphere, carbon dioxide (二氧化碳) acts rather like a one-way mirror—the glass in the roof of a greenhouse which allows the sun′s rays to enter but prevents the heat from escaping.According to a weather expert′s prediction, the atmosphere will be 3℃ warmer in the year 2050 than it is today, if man continues to burn fuels at the present rate. If this warming up took place, the ice caps in the poles would begin to melt, thus raising sea level several metres and severely flooding coastal cities, Also, the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere, possibly resulting in an alteration of the earth′s-chief food-growing zones.

　　In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet. But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of warming: in other words, by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels. Satellite pictures show that large areas of Antarctic ice are already disappearing. The evidence available suggests that a warming has taken place. This fits the theory that carbon dioxide warms the earth.

　　However, most of the fuel is burnt in the northern hemisphere,where temperatures seem to be falling. Scientists conclude,therefore, that up to now natural influences on the weather have exceeded those caused by man. The question is: Which natural cause has most effect on the weather?

　　One possibility is the variable behavior of the sun. Astronomers at one research station have studied the hot spots and "cold" spots(that is, the relatively less hot spots) on the sun.As the sun rotates, every 27.5 days, it presents hotter or "colder" faces to the earth, and different cet6w.com parts of the earth. This seems to have a considerable effect on the distribution of the earth′s atmospheric pressure, and consequently on wind circulation. The sun is also variable over a long term: its heat output goes up and down in cycles, the latest trend being downward.

　　Scientists are now finding mutual relations between models or solar-weather interactions and the actual climate over many thousand of years, including the last Ice Age. The problem is that the models are predicting that the world should be entering a new Ice Age and it is not. One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia of the earth′s climate. If this is right, the warming effect of carbon dioxide might thus be serving as a useful counter-balance to the sun′s diminishing heat.

　　26. It can be concluded that a concentration of carbon dioxide in the atmosphere would .

　　A) prevent the sun′s rays from reaching the earth′s surface

　　B) mean a warming up in the Arctic

　　C) account for great changes in the climate in the northern hemisphere

　　D) raise the temperature of the earth′s surface

　　27. The article was written to explain .

　　A) the greenhouse effect

　　B) the solar effects on the earth

　　C) the models of solarweather interactions

　　D) the causes affecting weather

　　28. Although the fuel consumption is greater in the northern hemisphere, temperatures there seem to be falling. This is .

　　A) mainly because the levels of carbon dioxide are rising

　　B) possibly because the ice caps in the poles are melting

　　C) exclusively due to the effect of the inertia of the earth′s climate

　　D) partly due to variations in the output of solar energy

　　29. On the basis of their models, scientists are of the opinion that .

　　A) the climate of the world should be becoming cooler

　　B) it will take thousands of years fro the inertia of the earth′s climate to take effect

　　C) the manmade warming effect helps to increase the solar effect

　　D) the new Ice Age will be delayed by the greenhouse effect

　　30. If the assumption about the delay of a new Ice Age is correct, .

　　A)the best way to overcome the cooling effect would be to burn more fuels

　　B) ice would soon cover the northern hemisphere

　　C) the increased levels of carbon dioxide in the atmosphere could warm up the earth even more quickly

　　D)the greenhouse effect could work to the advantage of the earth

　　26. 文章第一段讲到二氧化碳在大气中就像温室的玻璃屋顶一样吸收太阳的光线并阻挡光热的流失，文章第三段最后一句话又再次提到二氧化碳能使地球变热的理论。因此，正确答案为D)。

　　27. 全文讲述的是影响天气的诸多原因。选项A)，B)，C)在文中均被提及但不足以概括全文的主旨，只有D)是比较全面的。

　　28. 文章第四段提及这一现象时讲到，科学家们认为： 这一现象的产生是因为到目前为止自然界对天气的影响要大于人类对天气的影响。而究竟是哪种自然力量对天气的影响最大呢? 文章第五段第一句话给出了答案：其中一个可能就是太阳的不断变动。选项D)与此意相符。

　　29. 文章最后一段提到科学家们模拟太阳与天气之间的相互作用，并试图找出这种模拟与数千年来真正的气候之间的相互关系。此段第二句讲到：这些模拟结果都预测全球会进入一个新的冰河时代。所以，选项A)应为正确答案。

　　30. 本题涉及对文章最后一段最后一句话的理解。 如果有关太阳光能延缓新冰河时代到来的推测是正确的，那么二氧化碳的温室效应将发挥有效的作用来平衡太阳日益减少的光热。选项D)与此意相符。