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问题 单项选择题

某等距连续变量数列，其末组为开口组，下限为200，又知其邻组的组中值为170，则末组组中值为（ ）。

A．260

B．215

C．230

D．285

答案

参考答案：C

选择题

某理想变压器原、副线圈的匝数比为55∶9，原线圈所接电源电压按图示规律变化，副线圈接有一灯泡，此时灯泡消耗的功率为40 W，则下列判断正确的是(　　)

图13-9

A．副线圈两端输出的电压为

B．原线圈中电流表的示数约为0.18 A

C．变压器的输入、输出功率之比为55∶9

D．原线圈两端电压的瞬时值表达式为u=220sin100πt(V)
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单项选择题

Woman: Doctor, what’s wrong with my father

Man: He’s in pretty good shape, considering.

Question: What do we learn from the dialogue().

A. Her father is very sick.

B. There is nothing serious with her father.

C. Her father is an athlete.

D. The man is not sure about her father’s condition.
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