问题 单项选择题 A1型题

免疫应答的基本过程包括()

A.识别、活化、应答三个阶段

B.识别、活化、排斥三个阶段

C.识别、活化、反应三个阶段

D.识别、活化、增殖三个阶段

E.识别、活化、效应三个阶段

答案

参考答案:E

解析:

免疫应答的过程:

①识别,抗原的加工和识别在这一阶段完成;

②活化,T淋巴细胞或B淋巴细胞在识别抗原后,经复杂的信号传递被激活,增殖分化为效应细胞,产生效应分子(细胞因子、抗体);

③效应分子和效应细胞在多种体液及细胞成分的配合下将抗原物质清除。

填空题


International free trade occurs when there are no barriers to trade. Countries can get a lot of benefits from free trade. (31) , all countries choose to adopt protection policies to some extent In this essay, I will give (32) of the arguments in favour of world free trade, describe the methods for the trade protection policies (33) countries erect to protect domestic industries and give the arguments which can be put (34) to justify protectionist policies.
Tariffs are taxes on (35) products. Sometimes, tariffs are known (36) imports duties and customs duties. They can be used (37) raise revenue. But, they are usually used to (38) imports and also to help domestic producers. The effect of imposing (39) tariff is to raise price for domestic consumers, and some consumers will switch consumption (40) imported goods to domestically produced substitutes. (41) are two types of tariffs. One is percentage taxes, it is based on
percentage of value of goods. (42) one is specific (fixed sum taxes), it is based on a fixed tax (43) unit or weight. Quota is a limit on the supply of goods or services. It can be imposed on exports. The domestic market share will increase because of (44) a limit on the quantity of imported goods. However, the price of protected goods will also rise because a quota is to reduce supply. Voluntary export restraint or restriction (45) similar to a quota, but this time the limit on imports arises from a voluntary agreement (46) the exporting and importing countries. For example, the UK had an agreement with Japanese car (47) that they should not take (48) than 10 percent of the UK car market. Exchange control means that a government control on foreign currency controls importers access to foreign currency. This is a (49) which was used by a number of European countries, (50) the UK, in the 1960s and 1970s and is still found in some developing countries.

单项选择题