在人们提高危机认识中，成本最高但认识最为深刻的一条途径是（） A.案例分析 B.科学

如图，内壁光滑的薄壁圆钢管竖直固定在水平地面上。钢管的高为h=5.0m，横截面直径为d=2.0m。一只小球从钢管顶端的A点以初速度v₀沿钢管顶面圆的直径方向抛出，运动过程中依次跟钢管内壁的B、C两点相碰（碰撞前后瞬间速度大小不变，碰撞时间极短可以忽略不计），然后恰好落在底面圆的圆心D处。则小球从由A点抛出到落在D点所经历的时间t =         秒，A、C两点间的距离L=          米。

阅读理解

     As civilization proceeds in the direction of technology, it passes the point of supplying all the basic

essentials of life-food, shelter, clothes and warmth. Then we are faced with a choice between using

technology to provide and fulfill needs which have now been regarded as unnecessary or, on the other

hand, using technology to reduce the number of hours of work which a man must do in order to earn a

given standard of living. In other words, we either raise our standard of living above that necessary for

comfort and happiness or we leave it at this level and work shorter hours.

     I shall take it for granted that mankind has, by that time, chosen the latter alternative. Men will be

working shorter and shorter hours in their paid employment. It follows that the housewife will also expect

to be able to have more leisure in her life without lowering her standard of living. It also follows that

human domestic servants will have completely ceased to exist. Yet the great majority of the housewives

will wish to be relieved completely from the routine operations of the home such as scrubbing the floors

or the bath of the cooker, or washing the clothes or washing up, or dusting or sweeping, or making beds.

      By far the most logical step to relieve the housewife of routine is to provide a robot which can be

trained to the requirements of a particular home and can be programmed to carry out half a dozen or

more standard operations, when switched by the housewife.

1. As civilization develops in the direction of technology,________.

A. the basic essentials of life must be supplied

B. it is important to supply the basic essentials of life

C. it is no longer so important as it was in the past to supply all the basic essentials of life

D. it is not necessary to supply the basic essentials of life

2. According to the author, we are faced with________.

A. the choice of providing and fulfilling our needs

B. the choice of using technology

C. the choice of earning a standard of living

D. a choice between using technology to provide and fulfill needs to reduce the number of working hours

3. What alternative will mankind have chosen in future?

A. To leave our standard of living at this level and work shorter hours.

B. To raise our standard of living.

C. To fulfill needs which have been regarded as unnecessary.

D. To lower our standard of living and work shorter hours.

4. Now most housewives wish to________.

A. stop doing their housework

B. do more housework to improve their life

C. get rid of the heavy burden of their housework

D. do only simple and light housework

有机磷农药中毒导致肺水肿的主要解救用药是

A．西地兰

B．阿托品

C．解磷定

D．安定(地西泮)

E．地塞米松

铸铁件表面、棱角和凸缘处硬度较高，难以机械加工，为什么？如何处理？

压滤机入料粒度一般为0.1㎜以下。