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问题 单项选择题

有正吸高的自吸离心泵不能产生足够大的真空度，水吸不上来，不会是因为（）。

A．初次使用泵内未灌水

B．轴封失效

C．密封环间隙过大

D．吸入管接头漏气

答案

参考答案：C

单项选择题

作用于空心线圈两端的正弦电压不变时，若在空心线圈中间插入铁芯，则通过线圈的电流（）

A.增加

B.减小

C.不变

D.交替增加或减小
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填空题

Press Photographers


Good press photographers must have an "eye" for news, (26) journalists must have a "nose" for a good story. They must be able to interpret a story and decide rapidly how they can take (27) of the best opportunities to take pictures. The most difficult part of a press photographer’s job is that he or she has to be able to (28) a complicated situation with just one photograph. They rarely have second (29) and must be able to take the required (30) very quickly. Indeed, speed is essential — if the photographs are not (31) for the printing deadline, they are very unlikely to be of any (32) .
Most press photographers begin (33) with a local newspaper. There, the (34) is mostly for material of regional interest. Photographers may be expected to photograph a lot of unexciting events but to (35) the enthusiasm to put "something special" into every picture.
There is (36) competition among those who want to move from local to national newspapers. Here, the work is much more centered on news. The photographer must work (37) greater pressure and (38) more responsibility. Only (39) reliable, talented and resourceful photographers (40) this difficult move. The work is tough and can be (41) . On an overseas assignment, photographers may have to (42) unfamiliar food and accommodation, physical and mental stress, and (43) difficulty in transporting the pictures from an isolated area to get them to the newspaper (44) They also have to (45) the competition from other publications.

A. chances B. occasionsC. possibilitiesD. moments
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