常见的窒息性气体有哪些？

Scientific experiments can sometimes go wrong and when they do the results may range from the disastrous to the troubling. One such experiment took place in South America about fifty years ago. Whether its final consequences will cause serious damage or nothing more than a small trouble still remains to be seen.

The story began in 1956 when an American scientist working in Brazil decided to solve the problem of increasing the productivity of that country’s bees. He imported a very active type of African bee from Tanzania and mated (交配)it with the more easy-going native variety to produce a new kind of bees. The new bees worked harder and produced twice as much honey. It seemed that Professor Kerr, for that was the scientist's name, had a total success on his hands.

Then things began to go wrong. For some reason as yet unseen, but perhaps as a result of something in their environment, the new bees began to develop extremely attacking personalities. They became bad-tempered and easy to be angry, attacked the native bees and drove them from their living places.

But worse was to follow. Having taken over the countryside, the new bees, with their dangerous stings (叮) , began to attack its neighbors -- cats, dogs, horses, chickens and finally man himself. A long period of terror began that has so far killed a great number of animals and about 150 human beings.

This would have been bad enough if the bees had stayed in Brazil. But now they are on the move, heading northwards in countless millions towards Central and North America, and moving at the alarming speed of 200 miles a year. The countries that lie in their path are naturally worried because it looks as if nothing can be done to stop them.

小题1: The results of the South American experiment         .

A．are not yet certain

B．have proved to be wrong

C．have caused a serious trouble

D．are not important小题2: The experiment mentioned in this passage was designed to             .

A．make African bees less active

B．make Brazilian bees more easy-going

C．increase the number of bees in Brazil

D．increase the amount of honey in Brazil小题3: Which of the following may be the cause of the new bees' attacking personalities?

A．Their production of honey.

B．Their living environment.

C．Their hard work.

D．Their bad temper.小题4: The last paragraph implies that            .

A．the bees have been driven to Central and North America

B．the bees must be stopped from moving north

C．the bees may bring about trouble in more countries

D．the bees prefer to live in Brazil

1913年，章太炎为自己公开发布征婚广告（如图），它反映出当时

A．受社会各种因素的制约，依旧带有浓厚的保守思想

B．征婚成为当时社会主要的求偶方式，社会习俗发生重大变化

C．民主共和观念深入人心，婚姻自主成为一种时尚

D．婚姻礼俗开始删繁就简，仿效西方的新式婚礼

我国最近从国外引进一套设备，它可以有效地消除“白色污染”，它把回收的废旧塑料加工成汽油、煤油等。试分析在该加工过程中发生的主要反应类型为(    )

A．裂解

B．裂化

C．分馏

D．干馏

砂轮架在滑鞍上横向移动f横，可由手轮B机械驱动；粗进给时，手轮B转1转，砂轮横移量为（）mm，转1格进给（）mm；细进给时手轮B转1转，砂轮横移量为（）mm，转1格进（）mm。

微启式安全阀的开启高度为阀座喉径的（）。

A.1/40—1/20

B.1/4

C.1/10

D.1/20