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问题 选择题

醋酸溶液中存在电离平衡：CH3COOH⇌H++CH3COO-，下列叙述正确的是（　　）

A．醋酸溶液中离子浓度的关系满足：c（H+）=c（CH3COO-）

B．0.10mol/L的CH3COOH溶液加水稀释，溶液中c（OH-）减小

C．CH3COOH溶液中加入少量的CH3COONa固体，溶液中c（H+）减小

D．常温下，pH=3的CH3COOH溶液与pH=11的NaOH溶液等体积混合后，溶液的pH=7

答案

A．醋酸溶液中，氢离子包含醋酸电离和水电离的氢离子，醋酸根离子只有醋酸电离的，所以导致溶液中c（H+）＞c（CH3COO-），故A错误；

B．加水稀释醋酸溶液，能促进醋酸电离，溶液中氢离子浓度减小，温度不变，水的离子积常数不变，导致溶液中c（OH-）增大，故B错误；

C．加入少量CH3COONa固体，由电离平衡可知，c（CH3COO-）增大，抑制醋酸电离，所以溶液中c（H+）减小，故C正确；

D．常温下，pH=3的CH3COOH溶液中醋酸浓度大于10-3 mol/L，pH=11的NaOH溶液中氢氧化钠浓度等于10-3 mol/L，等体积混合时，导致酸过量，则溶液呈酸性，pH＜7，故D错误；

故选C．

单项选择题

According to the United States government, people are classified as homeless if they have no place to stay and no expectation of finding a place for the next thirty days, Although technically accurate, that is an impersonal assessment of an enormous and very human problem,
The homeless population represents all of us Americans, It includes men and women, the elderly, children, and infants. Its members are from all ethnic (种族的) groups. What they have in common is poverty.
Currently in the U.S., thirty-nine million people live in poverty. When money is really tight, paying the rent or buying food often becomes a choice. Government assistance in the form of food stamps does help but, as one homeless man explains, you can’t pay the rent with food stamps.
With no money for rent, the streets and homeless shelters become the alternative.

The U.S. government helps the homeless by ______.
A. giving them homeless allowancesB. giving them food stamps
C. finding jobs for them D. finding residences for them

Although men constitute the largest group within the homeless population, homeless women with children are rapidly joining them. In fact, one quarter of the homeless people in the U.S. are teenagers and young children.
People may become homeless for numerous reasons. However there are certain factors that many of these individuals have in common. They include a lack of adequate education and job skills. A majority of the teenagers and adults have not completed high school.
The abuse of alcohol and drugs is also a common factor. One third of the adult homeless population abuses alcohol, while one quarter of the same group uses drugs.
Some members of this population suffer mental health problems. Within the past several years many institutions for the menially ill have been closed and their patients sent "home". Unfortunately, a number of those people have no home to go to and they are unable to adequately look after themselves.
Job loss in today’s economy has also become a real factor in the loss of people’s homes. The breakup of families through abandonment and divorce are also contributing factors, particularly when there are children involved. The parent who is left to care for the kids with inadequate income may be forced to depend on the homeless shelters to put a roof over their heads.
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单项选择题

同申请复议的具体行政行为有利害关系的公民、法人或其他组织，经（）的批准，可作为第三人参加复议。

A.复议申请人

B.原行政机关

C.复议机关

D.人民法院
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