题干

物理小组的同学们练习安装照明电路,接通电源之前,老师将火线上的保险丝取下,把一个额定电压为220伏的灯泡作为检验灯泡连接在原来安装保险丝的位置,同时要求同学将电路中所有开关都断开。用这种方法可以检查电路中是否有短路,在接通电源后,下列说法中正确的是(    )

A:若检验灯泡正常发光,表明电路连接无误。

B:若检验灯泡不亮,但将某一个用电器的开关闭合后检验灯泡正常发光,表明这个开关的两端直接连到了火线和零线上。

C:检验灯泡不亮,但将某一个电灯的开关闭合后,这个电灯和检验灯泡都能发光,只是亮度都不够,这表明电路中出现了短路现象。

D:不论将电路中电灯的开关断开还是闭合,检验灯泡均不发光,表明电路中有短路。

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答案(点此获取答案解析)

B

同类题1

阅读下面的短文,从短文后各题所给的A、B、C和D四个选项中,选出可以填入空白处的最佳选项。

    “Daily Star, sir,” called Jason, carrying some news-papers under his arm. The little boy had been running up and down the street, but there were still twenty 1left. His voice was almost gone and his heart was 2. The shops would soon close, and all the people would go home. He would have to go home too, carrying the papers 3 money. He had hoped to sell more papers tonight to make more money to buy a 4for his mother and some seeds for his bird. That was why he had bought the papers with all his money. He 5 as he thought of his failure to sell all his papers.

    “You don't know the 6 of selling papers. You must shout, 'Hot news! Bomb bursting!'” another newsboy Chad told Jason. “7 it's not in the paper at all,” replied Jason. “Just run away quickly 8 they have time to see, and you'll 9out and get your money,” Chad said.

    It was a new 10 to Jason. He thought of his bird with no11and the cake he wanted to buy for his mother, but was12 that he would not tell a lie. Though he was 13 a poor newsboy, he had been 14 some good things.

    The next afternoon Jason went to the office for his papers15. Several boys were crowding around Chad, who declared with a 16 smile that he sold six dozen the day before. He added that Jason 17 money because he would not tell a lie. The boys 18 at Jason. “You wouldn't tell a lie yesterday, my boy?” A gentleman at the office came up and patted Jason's shoulder 19, “You're just the boy I am looking for.” A week later Jason started his new 20. He lost the sale of twenty papers because he would not tell a lie, but got a well-paid job because he told the truth.