生态平衡指生态系统中各种生物的种类、数量保持不变。（）

How often one hears children wishing they were grown-ups and old people wishing they were young again. Each age has its pleasures and its pains, and the happiest person is the one who enjoys what each age gives him without wasting his time in useless regrets(后悔).

Childhood is a time when there are few responsibilities to make life difficult. If a child has good parents, he is fed, looked after and loved, whatever he may do. It is impossible that he will ever again in his life be given so much without having to do anything in return. In addition, life is always presenting new things to the child — things that have lost their interest for older people because they are too well-known. But a child has his parents. He is not so free to do what he wishes to do; he is continually being told not to do things or being punished for what he has done wrong.

When the young man starts to earn his own living, he can no longer expect others to pay for his food, his clothes, and his room, but has to work if he wants to live comfortably. If he spends most of his time playing about in the way that he used to as a child, he will go hungry. And if he breaks the laws of society(社会) as he used to break the laws of his parents, he may go to prison. If, however, he works hard, keeps out of trouble and has good health, he can have the great happiness of building up for himself his own position in society.

小题1:After a child grows up, he __________.

A．will have little time playing

B．has to be successful in finding a job

C．can still ask for help in time of trouble

D．should be able to take care of himself小题2:Which of the following statements is NOT true according to the passage?

A．People are often satisfied with their life.

B．Life is less interesting for old people.

C．Adults are free to do what they want to do.

D．Adults should no longer rely on others.小题3:The underlined word "responsibilities" in the second paragraph means__________.

A．duties

B．jobs

C．suggestions

D．desires(渴望)小题4:The main idea of the passage is _________ .

A．life is not enjoyable since each age has some pains

B．young men can have the greatest happiness if they work hard

C．childhood is the most enjoyable time in one's life

D．one is the happiest if he can make good use of each age in his life

患者男。长期便秘，经检查诊断为继发性便秘。该患者便秘可能是由于（）

A.食物缺乏纤维素

B.工作紧张

C.结肠长

D.肠易激综合征

E.痔疮

缩余釉上皮可形成

A．牙釉质
B．龈沟上皮
C．附着龈
D．结合上皮
E．牙周膜

某县公安局两民警在侦办一件刑事案件中，对犯罪嫌疑人实施殴打致其死亡，两民警被依法追究刑事责任。犯罪嫌疑人的儿子申请国家赔偿，（）

A.应首先向该县公安局申请对殴打致死行为进行违法确认

B.两民警被追究刑事责任的法律文书就是确认文书

C.缺乏主体资格

D.之前应先向两民警提起附带民事诉讼

简述频率校正突发脉冲序列（FB）的组成。