工程测量仪器中，对水平角和竖直角进行测量的一种仪器是（）。A．水准仪B．电磁波测距仪 C．

Questions 21 to 25 are based on the following passage.

How often one hears children wishing they were grown up, 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.

Childhood is a time when there are few responsibilities. If a child has good parents, he is well fed, looked after and loved. It is unlikely 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. A child finds pleasure in playing in the rain, or in the snow. His first visit to the seaside is a marvelous adventure．But a child has his pains：he is not so free to do as he wishes as he thinks older people are; he is continually being told what to do and what not to do．Therefore, a child is not happy as he wishes to be.

When the young man starts to earn his own living, he becomes free from the discipline of school and parents; but at the same time he is forced to accept．responsibilities. With no one to pay for his food, his clothes, or his room, he 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 as he used to break the laws of his parents, he may get himself into trouble. If, however, he works hard, goes by the law and has good health, he may feel satisfied in seeing himself make steady progress in his job and in building up for himself his own position in society.

Old age has always been thought of as the worst age to be; but it is not necessary for the old to be unhappy. With old age comes wisdom and the ability to help others with advice wisely given. The old can have the joy of seeing their children making progress in life; they can watch their grandchildren growing up around them; and, perhaps best of all, they can, if their life has been a useful one, feel the happiness of having come through the battle of life safely and of having reached a time when they can lie back and rest, leaving everything to others.

21．The happiest people should be those who

A．face up to difficulties in life

B．hope to be young again

C．enjoy life in different ages

D．wish to be grown up

A．older people

B．new things

C．children

D．interests

A．he can not do whatever he wants to

B．he is not allowed to play in rain

C．he has a lot of new things to learn

D. he can not play at the seaside freely

A．live comfortably

B．take responsibilities

C．make progress in job

D．impress the society

A．Pains and Ages

B．Differences in Ages

C．The Best Age to Be

D．Happiness and Ages