问题 选择题

“a≠b或c≠d”是“a+c≠b+d”的(  )

A.充分而不必要条件

B.必要而不充分条件

C.充要条件

D.既不充分又不必要条件

答案

∵由于1≠2,4≠3,但1+4=2+3,∴“若a≠b或c≠d,则a+c≠b+d”为假命题;

∵由于1+2≠1+3,则1=1且2=3错误,∴“若a+c≠b+d,则a≠b或c≠d”为真命题.

所以“a≠b或c≠d”是“a+c≠b+d”的必要不充分条件.

故答案为B.

解答题
阅读理解

阅读理解。

     Tom was one of the brightest boys in the year, with supportive parents. But when he was 15 he suddenly

stopped trying. He left school at 16 with only two scores for secondary school subjects. One of the reasons

that made it cool for him not to care was the power of his peer (同龄人) group.

     The lack of right male (男性的) role models in many of their lives - at home and particularly in the school

environment (环境)-means that their peers are the only people they have to judge themselves against.

     They don't see men succeeding in society so it doesn't occur to them that they could make something of

themselves. Without male teachers as a role model, the effect of peer actions and street culture (文化) is all-

powerful. Boys want to be part of a club. However, schools can provide the environment for change, and

provide the right role models for them. Teachers need to be trained to stop that but not in front of a child's

peers. You have to do it one to one, because that is when you see the real child.

     It's pointless sending a child home if he or she has done wrong. They see it as a welcome day off to watch

television or play computer games. Instead, schools should have a special unit where a child who has done

wrong goes for the day and gets advice about his problems - somewhere he can work away from his peers

and go home after the other children.

1. Why did Tom give up studying? 

A. He disliked his teachers.

B. His parents no longer supported him.

C. It's cool for boys of his age not to care about studies.

D. There were too many subjects in his secondary school.

2. What seems to have a bad effect on students like Tom?

A. Peer groups.

B. A special unit.

C. The student judges.

D. The home environment.

3. What should schools do to help the problem schoolboys?

A. Wait for their change patiently.

B. Train leaders of their peer groups.

C. Stop the development of street culture.

D. Give them lessons in a separate area.

4. A teacher's work is most effective with a schoolboy when he _____.

A. is with the boy alone

B. teaches the boy a lesson

C. sends the boy home as punishment

D. works together with another teacher