正闪是地面正电荷的放电。

马克思逝世后，恩格斯独自担负起指导国际工人运动的任务，并在理论研究上全面丰富和发展了马克思主义。下列各项，属于在马克思逝世后的恩格斯的主要活动的有①写作《 * * 党宣言》 ②指导和推动第二国际成立 ③撰写《家族、私有制和国家的起源》 ④深入研究和探讨了19世纪末期资本主义经济政治发展中的一些新现象

A．①②③

B．②③④

C．①②④

D．①③④

不同区域范围内环境污染和资源破坏损失的变化率与相对的人口密度变化率之比是 ( )。

A．人口流密度

B．人口流强度

C．人口密度约束系数

D．环境约束系数

局域网的拓扑结构中，每个站由点到点链路连接到公共中心，任意两个站间通信均要通过公共中心的是()。

A．星型

B．环型

C．总线型

D．树型

According to the American Automobile（car）Association, since 1964 all cars sold in the United States have been equipped with seat belts（带子）(They are also called safety belts) Many studies of car accidents have shown that safety belts can save lives. One study showed that forty percent of those killed in car accidents could have been saved if they have been wearing seat belts.

Unfortunately seat belts are worn only by a small number of drivers and passengers    about fifteen percent in cities and only nine percent in small towns. And safety belt can not protect people who do not wear them.

In order to find out what kinds of people do wear seat belts, a study was made in several cities in of the United States. The following facts were learned about those who use their safety belts.

1. They do not smoke while driving.

2. They had more education than less educated people

3. They know some one who was hurt(but not killed) in an accident

Advertisements based on these facts have been printed in newspapers and magazines in order to teach people the importance of using seat belt. But these advertisements have not helped much. Some people believe there should be a law ordering drivers and passengers to use safety belts. In Australia, where there is such a law, death in car accidents have reduced to twenty-four percent.

小题1: Seat belts                                 

A．are safe clothes car drivers usually wear when they drive.

B．Are belts that are used to tie drivers’ hands when they drive

C．Have been worn by all drivers in the united States since 1964

D．Are something that protect drivers from injury in car accidents.小题2:“One study showed that…” Here “study” means       

A．lesson

B．exam

C．research

D．education小题3:Which of the following sentences is NOT true？

A．More drivers in the country wear seat belts.

B．More educated people in the United States wear seat belts.

C．Much has been done to advise drivers to wear safety belts.

D．About three-twentieths of the drivers wear seat belts.小题4:Which of the following is true?

A．Most people who do wear seats smoke while driving.

B．When it is hot, people don’t have to wear their seat belts.

C．A law was made in Australia that only those who don’t smoke can drive a car

D．Some people agree that those who do not wear seat belts while driving should pay money for it.小题5:What is the best title of the passage?

A．Seat belts

B．Who wear seat belts

C．A study on seat belts

D．A law and safety belts

沉积岩相