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问题 多选题
如图为理想变压器原线圈所接交流电压的波形．原、副线圈匝数比n1：n2=10：1，串联在原线圈电路中电流表的示数为1A，下列说法正确的是（　　）

A．变压器输出端所接电压表的示数为20V

B．变压器的输出功率为200W

C．变压器输出端的交流电的频率为50Hz

D．穿过变压器铁芯的磁通量变化率的最大值为20/n2Wb/s

答案

BCD

补全对话，情景问答
根据对话内容，选用方框中适当的句子补全对话。
A. Which bus goes to the hospital?
B. This little girl brought me here.
C. You can take a bus.
D. The No. 3 bus will take you there.
E. Let's ask this policeman.
F. It'll take you about half an hour.
G. We'd better take a bus.

A: How can I get there? I don't know the way. 　　
B: 1.            He may know. Excuse me! Which is the way to the North Hospital? 　　
C: Go down this street until you reach the second traffic lights. Turn right. At he end of the road you'll see
    the hospital. 2.             　　
B: Half an hour? That's too long! Is there a bus? 　　
C: Yes. 3.             　　
B: Thanks a lot. Granny, the hospital is not very near. 4.            I'll go with you. 　　
A: How kind! Thank you. 　　
(Twenty minutes later. In the hospital the woman finds her husband.)　　
D: But how did you get here? 　　
A: By bus. 5.            　　
D: Which girl? I must thank her!
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问答题 简答题

一般情况下，燃烧法鉴别纤维时，纤维素纤维、蛋白质纤维和合成纤维各有什么明显特征？
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