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____.
○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
39. 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 for the inertia of modern city. In the home, many labour-saving devices are p_____51_____ by electricity.
Even when we turn o______52____ the beside lamp and fast asleep, electricity is working for us, driving our refrigerators, heating our water, or k_____53____ our rooms air-conditioned. Every day, trains, trolley-buses and trams take us to and from work. We rarely b____54____ to consider why or how they run-until something goes w____55____.
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