闸瓦制动式也称()。A.电动摩擦式 B.电动可逆式 C.双筒卷扬式 _爱下问搜题

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问题单项选择题

闸瓦制动式也称()。

A.电动摩擦式

B.电动可逆式

C.双筒卷扬式

D.摩擦离合式

答案

参考答案：B

解析：按传动形式，卷扬机可分为电动可逆式(闸瓦制动式)和电动摩擦式(摩擦离合器式)。故选B。

问答题论述题

论述社会学传入中国的背景。

填空题

World Water Shortage

A new study warns that about thirty percent of the world’s people may not have enough water by the year 2025.
A private American organization called (1) Action International did the new study. It says (2) than three-hundred-thirty-five-million people (3) enough water now. The people live in twenty-eight (4) . Most of the countries are in Africa or the (5) East.
P-A-I researcher Robert Engelman says (6) the year 2025, about three-thousand-million people (7) lack water. At least 18 more countries are (8) to have severe water problems. The demand (9) water keeps increasing. Yet the amount of water on Earth (10) the same.
Mr. Engelman says the population in countries that lack water is (11) faster than in other parts of the world. He says (12) growth in these countries will continue to (13) .
The report says lack of water in the future may (14) in several problems. It may increase health (15) . Lack of water often means drinking (16) not safe. Mr. Engelman says there are problems (17) over the world because of diseases, such as cholera, (18) are carried in water. Lack of water may also result (19) more international conflict. Countries may have to (20) for water in the future. Some countries now get sixty percent of their fresh water from other countries. This is true of Egypt, the Netherlands, Cambodia, Syria, Sudan, and Iraq. And the report says lack of water would affect the ability of developing to improve their economies. This is because new industries often need a large amount of water when they are beginning.