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问题 选择题

如图甲把锌片和铜片用导线相连后插入稀硫酸溶液构成原电池。某实验兴趣小组做完实验后，在读书卡上的记录如图乙所示，则卡片上的描述合理的是

[ ]

A．①②③

B．②④

C．④⑤⑥

D．③④⑤

答案

答案：B

单项选择题

Microwave communication uses high-frequency (56) waves that travel in straightlines through the air. Because the waves cannot (57) with the curvature of the earth, they can be (58) only over short distance. Thus, microwave is a good (59) for sending data between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of "dishes" or (60) .These can be installed on towers, high buildings, and mountain tops.

A．material

B．equipment

C．medium

D．channel
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单项选择题

废热锅炉发汽蒸汽压力≤（）MPa。

A.1.8

B.3.5

C.1.0

D.0.8
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