题干

在由电源、导线、两个开关、两只灯泡组成的电路中,下列关于电路中两只灯泡的串并联判断,说法正确的是(   )

A:一个开关闭合,另一个开关断开,一只灯亮,另一只灯不亮,则两灯一定是并联

B:一个开关闭合,另一个开关断开,两灯都不亮,则两灯一定是串联

C:两个开关都闭合,如果两灯通过的电流相等,则两灯一定是串联

D:两个开关都闭合,如果两灯两端的电压相等,则两灯一定是并联

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答案(点此获取答案解析)

A

同类题2

阅读下列短文,从短文后各题所给的四个选项(A, B, C和D)中,选出可以填入空白处的最佳选项。

    I went with some colleagues from my office for a dinner in a very popular local restaurant. It was 1 business time and the restaurant was packed. We 2 found a table in a corner for three of us.

    As soon as we sat down, we heard a crash when a cleaning boy 3 the floor with all the plates he was carrying. There was 4 and no one was saying or doing anything.

    In a flash I remembered my 5 many years ago. Once, I 6 in the airport because I had rushed there on my own on an empty stomach. I was picked up and taken care of by two 7. Now this was my chance to 8 it forward.

    I ran to the young man's side immediately, turned him on his back and screamed for someone to 9 a hot drink. Soon people started asking if I was a doctor. I said I was not, 10 I was skillful at blacking out(晕厥).

    The kid soon opened his eyes, 11 what had happened. I 12 him by saying it was OK and I had had a 13 experience. He had not eaten anything. I held the 14 drink to his mouth till he finished it and sat with him till he felt OK.By then the 15 had arrived. I asked her to give the kid something to eat. I offered to pay.

    The manager was kind enough to refuse the 16 and agreed to make sure the kid ate before he went home. By the time all this was 17 it was getting late for my colleagues. We hadn't 18 anything yet, so they decided to go home.

    I slowly walked home, not hungry any more, feeling 19 for the opportunity I pay forward the 20 I had received many years ago.