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问题 填空题

请将下列物质按照一定的要求（或由高到低）排列（填序号）

（1）相对分子质量：①二氧化碳  ②氢气   ③氮气______；

（2）硫元素的化合价：①SO2②Na2SO4 ③H2S______；

（3）溶解性：①AgCl  ②Ca（OH）2 ③KNO3 ______．

答案

（1）相对分子质量为各元素相对原子的和；则三种物质的相对分子质量分别为：①二氧化碳44，②氢气2，③氮气28；所以相对分子质量从大到小：①③②；故答案为：①③②．

（2）根据在化合物中正负化合价代数和为零，硫元素在①SO2；②Na2SO4；③H2S中的化合价分别是

①x+（-2）×2=0，

②y+（+2）+（-2）×4=0，

③z+（+1）×2=0，

可得x=+4，y=+6，z=-2，

故答案为：②①③；

（3）根据溶解度可知KNO3的溶解度最大，Ca（OH）2微溶，AgCl难溶，故答案为：③②①．

单项选择题

最早用导尿术治疗小便不通见于

A．《内经》
B．《诸病源候论》
C．《备急千金要方》
D．《丹溪心法》
E．《景岳全书
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单项选择题

In choosing a friend, one should be very careful. A good friend can help you study. You can have fun together and make each other happy. Sometimes you will meet fair weather friends. They will be with you as long as you have money or luck, but when you are down, they will run away. How do I know when I have found a good friend I look for certain qualities of character, especially understanding, honesty and reliability.
Above all else, I look for understanding in a friend. A good friend tries to understand how another person is feeling. He is not quick to judge. Instead, he tries to learn from others. He puts himself in the other person’s place, and he tries to think of ways to be helpful. He is also a good listener.
At the same time, however, a good friend is honest. He does not look for faults in others. He notices their good points. In short, a friend will try to understand me and accept me.
Another quality of a friend is reliability. I can always depend on a good friend. If he tells me he will meet me somewhere at a certain time, I can be sure that he will be there. If I need a favor, he will do his best to help me. If I am in trouble, he will not run away from me.
There is a fourth quality that makes a friend special. A special friend is someone with whom we can have fun. We should enjoy our lives, and we would enjoy our friendship. That is why I especially like friends who are fun to be with. A good friend likes the same things I like. We share experience and learn from each other. A good friend has a good sense of humor, too. He likes to laugh with me. That is how we share in the joy of being friends. And I know that he is looking for the same quality in me.
When I meet someone who is reliable, honest, and understanding, I know I’ve found a friend!

Which of the following qualities the writer thinks is the most important in choosing a friend

A．Understanding.

B．Honesty.

C．Reliability.

D．A sense of humor.
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