Passage Four
Questions 36 to 40 are based on the following passage.
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 warm 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 rotated, every 27.5 days, it presents hotter or “colder” faces to the earth, and different aspects to different 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 of solar-weather interactions and the actual climate over many thousands 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.
36. Experts used to believe that the chief reason for global warming is          .
A) that most fuel is consumed in the northern hemisphere
B) human activities来源：www.examda.com
C) natural influences and carbon dioxide
D) the solar energy
37. The article is written to illustrate          .来源：www.examda.com
A) the greenhouse effect
B) the solar effects on the earth
C) the models of solar-weather interactions
D) the factors responsible for the global climate
38. In spite of the greater consumption of fuel in the northern hemisphere, temperatures seem to be falling. This is          .
A) possibly because of the melting of the ice caps in the poles
B) mainly because the levels of carbon dioxide are rising
C) partly due to the variations of the output of solar energy
D) because the sun presents its “colder” face to the earth
39. On the basis of the models, scientists are of the opinion that          .
A) the climate of the world should be becoming cooler
B) it’ll take thousands of years for the inertia of the earth’s climate to take effect
C) the man-made warming effect helps to increase the solar effects
D) the new Ice Age will be delayed by the greenhouse effect
40. If the assumption about the delay of a new Ice Age is correct          .来源：www.examda.com
A) the increased levels of carbon dioxide will warm up the earth even more quickly
B) the greenhouse effect will work to the advantage of the earth
C) the best way to overcome the cooling effect will be to burn more fuels
D) ice will soon cover the northern hemisphere