问题 单项选择题

细菌外毒素的特性是

A.对组织有选择性
B.主要由革兰阴性菌产生
C.主要成分是脂多糖
D.抗原性不强
E.不能转化为类毒素

答案

参考答案:A

解析:外毒素是细菌生长繁殖过程中在菌细胞内合成后分泌到细胞外的毒性物质,产生菌主要是革兰阳性菌。外毒素抗原性强,经甲醛处理可转变为类毒素。不同种细菌产生的外毒素对机体的毒性作用明显不同,可选择性地作用于某些组织器官,引起特殊病变。

阅读理解

People who like travelling have their reasons. They believe that travelling can help them expand their field of view, especially in the geographical and historical sense. They also think that touring will give them more chances to enjoy different kinds of food and experience new things that would never be brought by other activities. But those who dislike travelling also have some reasons.

Travelling, in my opinion, does more good than harm. Most importantly, it broadens(扩大) our mind. We can get in touch with other civilizations(文明), culture, customs and ideas.

Through history, most people travelled because of necessity(必要性)—not for pleasure. People travelled just in order to remain alive. They searched for food to eat or places to live in. They sometimes ran away from enemies. This is not to say that no one ever travelled just for the fun of it. In ancient times, for example, rich Romans travelled all the way to Greece to take part in the Olympic Games, and festivals. Of course, some people decided to travel just out of curiosity(好奇心). They wanted to find out what it looked like beyond the horizon(地平线). Also, business travel has been going on for centuries.Traders could not only make money but also learn to speak several languages and be introduced to different cultures.

So travelling does enrich our mind and draw new ideas to us. There is no doubt that we can get much from it.

小题1:The underlined word“expand”in Paragraph 1 can be replaced by “ __________”.

A.decide

B.protect

C.widen

D.lose小题2:According to the passage, in the past most people travelled _____________.

A.for knowledge

B.to make a living

C.to get experiences

D.for fun小题3:In the writer’s opinion, travelling can be ______________.

A.tiring

B.funny

C.expensive

D.helpful

多项选择题