在运行中的二次回路上工作时，必须由一人操作，另一人作监护。监护人应由技术经验水平较高

下列常见的物质中，由原子直接构成的是①铜  ②水  ③氧气   ④食盐（　　）

A．①

B．①

C．①④

D．①②

从距水平面高度为h处的A点水平抛出一个小球，抛出时的速度为v．再在A点的正下方距地面高度为h/2处以同样方向的水平速度2v将小球抛出．若空气阻力可忽略不计，则以下说法正确的是（　　）

A．两次小球的运动轨迹在空中不会相交

B．两次小球的运动轨迹在空中一定相交

C．第二次小球在空中运动的时间是第一次的一半

D．第二次小球在落地时的水平位移是第一次的2倍

绘制工艺流程图时，为避免管线与设备之间发生重叠，通常把管线画在设备的（）。

A、上方

B、下方

C、上方或下方

D、中间

阅读理解

     Ask a bachelor(单身汉) why he resists marriage even though he finds dating to be less and less

satisfying. If he is honest he will tell you that he is afraid of making a commitment. For commitment is in fact quite painful. The single life is filled with fun, adventure, excitement. Marriage has such moments, but they

are not its most distinguishing (显著的) features.

     Couples with infant children are lucky to get a whole night's sleep or a three-day vacation. I don't know any parent who would choose the word fun to describe raising children. But couples who decide not to

have children never know the joys of watching a child grow up or of playing with a grandchild.

     Understanding and accepting that true happiness has nothing to do with fun is one of the most liberating realizations. It liberates (释放) time: now we can devote more hours to activities that can genuinely

increase our happiness. It liberates money: buying that new car or those fancy clothes that will do nothing

to increase our happiness now seems pointless. And it liberates us from envy: we now understand that all

those who are always having so much fun actually may not be happy at all.

1. According to the author, a bachelor resists marriage chiefly because ________ .

A. he is reluctant to take on family responsibilities

B. he believes that life will be more cheerful if he remains single

C. he finds more fun in dating than in marriage

D. he fears it will put an end to all his fun adventure and excitement

2. Raising children, in the author's opinion is ________ .

A. a moral duty    

B. a thankless job

C. a rewarding task

D. a source of inevitable pain

3. From the last paragraph, we learn that envy sometimes stems from (起源于) ________ .

A. hatred          

B. misunderstanding

C. prejudice          

D. ignorance

4. To understand what true happiness is one must ________ .

A. have as much fun as possible during one's lifetime

B. make every effort to liberate oneself from pain

C. put up with pain under all circumstances

D. be able to distinguish happiness from fun

我国志愿服务的特点。