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问题 单项选择题

胶皮水击泄压阀的氮封压力用“p1”表示，当进站干线压力p2＜p1时，则胶皮套管紧套在内套管的外壁上，此时胶皮水击泄压阀不通。当p2＞p1时，胶皮套管压盖在的p3=p2-p1作用下被顶离内套馆外壁，从而使胶皮水击泄压阀打开，进站干线的部分原油便从右端流到左端而（），使来油压力逐渐降低，自动防止泵进口管的超压。

A.泄到管外

B.泄到站外

C.泄到泵站出口

D.泄到大罐

答案

参考答案：D

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.
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问答题

在人民教育出版社现行高中生物教科书中“比较过氧化氢在不同条件下的分解”的实验中，编者设计了这样的实验步骤：“1．取四支洁净的试管，编上序号1、2、3、4，并各注入2mL过氧化氢溶液。2．将2号试管放在90℃左右的水浴中加热。3．向3号试管内滴入2滴氯化铁溶液。向4号试管内滴入2滴肝脏研磨液。”请问该实验步骤中的对照属于何种类型的对照其意义何在
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