在配电设计中，通常采用( )的最大平均负荷作为按发热条件选择

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问题单项选择题

在配电设计中，通常采用( )的最大平均负荷作为按发热条件选择电器或导体的依据。

A．20min
B．30min
C．60min
D．90min

答案

参考答案：B

解析：《工业与民用配电设计手册》第3版P1。

填空题

选出正确的单词或词组填空。

1. Mittens and __________ (mitt, mitts) are the same.

2. There are many __________ (peoples, people) at the restaurant.

3. He is a good __________ (sing, singer)

4. The TV is too loud. Please turn __________ (on, down) the TV.

5. It's cold. He is __________ (taking off, putting on) his coat.

6. I can play __________ (the piano, the football).

7. I think the girl is the __________ (good, best).

8. There are four __________ (season, seasons) in a year.

9. I like to sit __________ (under, in) the sun.

10. It's cold, Let's go __________ (outside, inside).

问答题简答题

纯锗，硅中掺入III或Ⅴ族元素后，为什么使半导体电学性能有很大的改变？杂质半导体（p型或n型）应用很广，但为什么我们很强调对半导体材料的提纯？