问题
选择题
— What's ____________?
— Sixty.[ ]
A. twenty-three and thirty-seven
B. twenty-four and twenty-seven
C. twenty-seven and thirty-four
D. twenty-seven and thirty
答案
答案：A
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— What's ____________?
— Sixty.[ ]
A. twenty-three and thirty-seven
B. twenty-four and twenty-seven
C. twenty-seven and thirty-four
D. twenty-seven and thirty
答案：A
，副线圈与阻值为R=200
的电阻相连，原线圈两端所加的电压
，则
