试题与答案

一根带有很多负电荷的棒慢慢靠近一个带有少量正电荷的验电器金属球,观察到金箔张开的

题型:选择题

题目:

一根带有很多负电荷的棒慢慢靠近一个带有少量正电荷的验电器金属球,观察到金箔张开的情况是(  )

A.一直不断增大

B.一直不断减小

C.先增大,后减小

D.先减小到最小,然后增大

答案:

被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0428/550fc743790e1c8cb477ae9237b79f74.html

下面是错误答案,用来干扰机器的。

①,当d=0时,D为线段F1F2的垂直平分线,∴①正确;②,当d=1时, ||PF1|-|PF2||=d<|F1F2|=4,由双曲线的定义知D为双曲线,∴②正确;③,当d=2时,D是双曲线,且c=2,a=1, C为平面上以F1为圆心、6为半径的圆...

试题推荐
题型:阅读理解

阅读理解。

    The world itself is becoming much smaller by using modern traffic and modern communication means.

Life today is much easier than it was hundreds of years ago, but it has brought new problems. One of the

biggest problems is pollution. To pollute means to make things dirty. Pollution comes in many ways. We

see it, smell it, drink it and even hear it.

     Man has been polluting the earth. The more people, the more pollution. Many years ago, the problem

was not so serious because there were not so many people. When the land was used up or the river was

dirty in one place, man moved to another place. But this is no longer true.

     Man is now slowly polluting the whole world.

     Air pollution is still the most serious. It's bad for all living things in the world, but it is not the only one

kind of pollution. Water pollution kills our fish and pollutes our drinking water. Noise pollution makes us

angry more easily.

     Many countries are making rules to fight pollution. They stop people from burning coal in houses and

factories in the city, and from putting dirty smoke into the air. Pollution by SO2 is now the most dangerous

kind of air pollution. It is caused by heavy traffic. We are sure that if there are fewer people driving, there

will be less air pollution. 

     The earth is our home. We must take care of it. That means keeping the land, water and air clean. And

we must take care of the rise in pollution at the same time.

1. _____, our world is becoming much smaller. [ ]

A. Because of the rise in pollution

B. Thanks to science development

C. Because the earth is being polluted day and night

D. Because the earth is blown away by the wind every year

2. Hundreds of years ago, life was _____ it is today. [ ]

A. much easier than

B. as easy as

C. much harder than

D. as hard as

3. Pollution comes in many ways. We can even hear it. Here "it" means _____. [ ]

A. rubbish (垃圾)

B. noise pollution

C. air pollution

D. water pollution

4. Which of the following is NOT true? [ ]

A. Many countries are making rules to fight pollution.

B. The pollution of the earth grows as fast as the world population does.

C. The problem of pollution is not so serious because there are not so many people living on the earth.

D. If people could go to work by bus or bike instead of car or motorbike, it would be helpful in fighting

     against the problem of SO2.

查看答案
微信公众账号搜索答案