问题 选择题

将编号为1,2,3,4,5的五个球放入编号为1,2,3,4,5的五个盒子,每个盒内放一个球,若恰好有两个球的编号与盒子编号相同,则不同的投放方法的种数为(  )

A.40种

B.30种

C.20种

D.10种

答案

首先选出两个盒子,使其编号与放入其中的球的编号相同,有C52=10种情况,

剩下的3个盒子中,其编号与放入其中的球的编号不同,有2种情况,

由分步计数原理,可得共2×10=20种情况;

故选C.

单项选择题
阅读理解

It was a very foggy day in London. The fog was so thick that it was impossible to see more than a foot or so. Buses, cars and taxis were not able to run and were standing by the side of the road. People were trying to find their way about on foot but were losing their way in the fog. Mr. Smith had a very important meeting at the House of Commons and had to get there but no one could take him. He tried to walk there but found he was quite lost. Suddenly he bumped into a stranger. The stranger asked if he could help him. Mr. Smith said he wanted to get to the Houses of Parliament. The stranger told him he would take him there. Mr. Smith thanked him and they started to walk there. The fog was getting thicker every minute but the stranger had no difficulty in finding the way. He went along one street, turned down another, crossed a square and at last after about half an hour’s walk they arrived at the Houses of Parliament. Mr. Smith couldn’t understand how the stranger found his way. “It is wonderful,” he said. “How do you find the way in the fog?”

“It is no trouble at all to me,” said the stranger, “I am blind.”

小题1:According to the passage, we can infer that “bump into” means _______.

A.knock off

B.meet by chance

C.strike

D.traffic accident小题2:Which of the following statements are NOT true?

A.The stranger has a better sight than Mr. Smith.

B.Heavy fog can cause traffic accidents.

C.It’s easy to get lost in a foggy day.

D.The fog was getting thicker and thicker.小题3:Why is it no trouble at all to the stranger to find the way in the fog?

A.Because he is a local inhabitant of London.

B.Because he lives next to the Houses of Parliament.

C.Because he is familiar with the route.

D.Because he finds the way not by sight but by heart.小题4:This article mainly tells us that ________.

A.London is a foggy city.

B.Mr. Smith works for the government.

C.A blind stranger led the way for Mr. Smith in a foggy day.

D.Mr. Smith had a very important meeting and lost his way in the fog.