问题 名词解释

Vi抗原

答案

参考答案:

Vi抗原是一种不耐热的酸性多糖的聚合体,存在于菌体的最表面,有抗吞噬和保护细菌免受相应O抗体凝集和补体的溶菌作用。在血清学检查时,需先加热破坏Vi抗原后,O抗原才能与O抗血清凝集。可用Vi噬菌体进行分型。

阅读理解

I will tell you the truth about plastic bags-the positive and the negative sides and provide a solution to this problem. Whether it is a shopping bag, a food bag or a trash bag, they are all made of plastic bags. Grocery store owners are very generous in using plastic bags. They place the fruit in one bag and drop the box of milk in another. Ever wonder why?

The positive side of plastic bags

Grocery stores, shopping centres, and restaurants are not thrifty in using and giving out plastic bags because they cost no more than a cent each, while a paper bag costs four cents. Plastic bags are produced so cheaply and massively(大量地)that they are used by 80% of store owners. In addition, they are light and very easy to carry and store.

The production of plastic bags has increased greatly over the last 20 years and producers of plastic bags are making large profits. However, the negative side of plastic bags is becoming well-known. More people are now getting worried that the earth is becoming a victim of the plastic bag success story.

The negative side of plastic bags

While production and consumption(消费)of plastic bags is good for business, it is not so for our Mother Earth. They have resulted in an increase in the amount of litter found floating in water or in the streets where we live.

Plastic storage bags, after usage, usually go to landfills(垃圾填埋地)as trash bags. They make the oceans poison sea animals. They give off toxins(毒素)when burned. They simply pollute the ground, air and water.

That is the true cost of plastic bags, and it looks like it is more than a cent. These are very alarming concerns and proper action needs to be taken.

小题1:According to Paragraph 3, plastic bag producers ________.

A.are now worried that the earth will become a victim of plastic bags

B.don’t think they have done enough to popularize plastic bags

C.have not realized the harm of plastic bags

D.have succeeded in popularizing the use of plastic bags小题2:From the last three paragraphs, we learn that         .

A.plastic bags harm the earth severely

B.most plastic bags are not made use of

C.the prices of plastic bags are reasonable

D.plastic bags are the leading polluter on the earth小题3:What will the writer most probably talk about in the following paragraph?

A.How plastic bags are produced.

B.How plastic bags are used.

C.How to popularize the use of paper bags.

D.How to solve the problems caused by plastic bags.

单项选择题