问题
选择题
钓鱼的人都知道，在河边不能高声讲话，否则会把水中的鱼惊跑，鱼能听到声音是由于（ ）
A．空气传递了声音
B．水传递了声音
C．空气和水传递了声音
D．鱼竿传递了声音
答案
因为固体、液体和气体都可以传播声音，当钓鱼时大声喧哗会把鱼吓跑，说明空气和水传递了声音．
故选C．
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钓鱼的人都知道，在河边不能高声讲话，否则会把水中的鱼惊跑，鱼能听到声音是由于（ ）
A．空气传递了声音
B．水传递了声音
C．空气和水传递了声音
D．鱼竿传递了声音
因为固体、液体和气体都可以传播声音，当钓鱼时大声喧哗会把鱼吓跑，说明空气和水传递了声音．
故选C．
In 1990 a report was published about what the earth might be like 20 years from then on. The report was a result of a three-year 36 . According to the report, the picture of the earth in the year 2010 is not a 37 one. The world will be more 38 because the population will continue to grow . The population could be 39 6 300 million, almost 2 115 million more than in 1985 .More people would move into cities, especially cities in 40 countries . Cities like Cairo and Jakarta probably would 41 have 15 million by then . Food production will 42 , but not enough to feed all the people . Farmers will grow 90% more food than they did in 1985, 43 most of the increase would be in countries that 44 produce enough food for their people . Little increase is 45 in South Asia, Africa and the Middle East . Poor farming ways are 46 large areas of crop land, changing farms into deserts . More farmland is 47 as cities become larger and more houses are built . 48 will get worse as industrial countries burn more coal and oil .Many of the world’s 49 could disappear as more and more trees are cut down . Energy will continue to be a serious problem . The experts say their picture of the earth for the year 2010 50 . They only carried out the situation that 51 today . By changing the situation, by 52 the problems, the picture can be changed . There is 53 time for the nations of the world to work 54 a plan of action . But they warned that 55 too long to make decisions would greatly reduce the chances of success .
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