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问题 选择题

分离氯化钠与硝酸钾的混合物，应采用的方法是（　　）

A．过滤B．蒸发结晶C．降温结晶

答案

KNO3和NaCl的溶解度受温度的影响不同，硝酸钾溶解度受温度影响较大，而氯化钠受温度影响较小；分离氯化钠与硝酸钾的混合物，可采取加热水溶解配成饱和溶液、冷却热饱和溶液（降温结晶）使KNO3先结晶出来、再过滤的方法．

故选C．

单项选择题

将E-R图转换到关系模式时，实体与联系都可以表示成_______。

A．属性

B．关系

C．键

D．域
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单项选择题

Congress makes the laws in the United States. It has two parts, which are more or less equal in power. They are known as the House of Representatives and the Senate. The House of Representatives is larger than the Senate whose 100 members (two from each state) serve for six years. The 435 members of the House are elected every two years, and the number from each state is determined by the population of the state. For example, California, which has a large population, has 43 representatives, while the State of Nevada has only one.
The House and Senate are divided into small groups which take care of special matters such as education or foreign affairs. The most important work of Congress is often done in these groups, which are called subcommittees.

In the U.S. Congress, the House of Representatives and the Senate are______.
A. not equal. The House is more powerful
B. almost equal in power
C. not equal. The Senate is far more powerful
D. different. The House is more important

According to the Constitution of the United States, a senator must be at least 30 years old and he must have been a citizen of the United States for nine years at the time of his election. To be elected to the House a person must be 25 years old and must have been a United States citizen for seven years. At the present time, members of Congress include businessmen, farmers, teachers, and especially lawyers. In general, senators are better known than representatives because they are fewer in number and serve for a longer time. Many American presidents served in Congress before they became president.
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