A、The Arctic. B、The West Antarctic. C、The northern hemisphere. D、The southern hemisphere. B文中谈到，在过去气象专家更多地关注北极而现在却更多地关注南极西部地区。因此

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 meters and severely flooding coastal cities. At the same time, the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere, possibly resulting in an alteration of 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. As a result, scientists conclude that up to now natural influences on the weather have exceeded those caused by human being.
19. According to the weather expert’s prediction, what will make the atmosphere warmer?
20. Which area is now paid more attention to by weather experts?
21. What’s the scientists’ conclusion about natural influences on the weather?