人眼可直接通过扫描电镜的目镜观察到图像。

按水利工程计价规范附录A，洞室石方开挖适用范围（）。

A.水平夹角≤6°的石方洞挖

B.水平夹角6°～75°的石方洞挖

C.水平夹角＞75°，深度大于上口短边或直径的石方井挖

D.开挖横断面较大，且轴线长度与宽度之比小于10的石方洞挖

阅读所给短文，并根据短文后题目的要求进行简答。(注意题后的字数要求)

     _____. Fifty years ago, only 4 out of every 100 people in the United States were 65 or older. Today, 10

out of every 100 Americans are over 65. The aging of the population will affect American society in many

ways: education, medicine, and business. Quietly, the growing of America has made it a very different society,

one in which people have a quite different idea of what kind of behavior is suitable at various ages.

     A person's age no longer tells you anything about his or her social position, marriage or health. There's no

longer a particular year in which one goes to school or goes to work or gets married or starts a family. The

social clock that kept us on time and told us when to go to school, get a job, or stop working isn't as strong

as it used to be. It doesn't surprise us to hear of a 29-year-old university president or a 35-year-old grandmother,

or a 70-year-old man who has become a father for the first time. Public ideas are changing.

     Many people say, "I am much younger than my mother or my father was at my age." No one says, "Act

your age" any more. We've stopped looking with surprise at older people who act in youthful ways.

1. What is mainly talked about in the passage? (Within 12 words)

    _____________________________________________________________________________

2. Which sentence in the passage can be replaced by the following one? We no longer feel astonished when

    older people behave as young people.

    _____________________________________________________________________________

3. Fill in the blank with proper word to complete the sentence. (Within 6 words)

    _____________________________________________________________________________

4. What does "Act your age" mean?

    _____________________________________________________________________________

5. Translate the underlined sentence into Chinese.

    _____________________________________________________________________________

下列表达式中正确的是( )。

A．5++

B．(a+++

C．++(a+

D．++x

为什么在畜禽饲料中要使用酶制剂？

柴油机的起动控制主要包括（）、（）、（）控制。