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问题 选择题

下列溶液中含Cl-浓度最大的是（　　）

A．5m1、0.1mol•L-1的AlC13溶液

B．10m1、0.1mo1•L-1的CaC12溶液

C．20m1、0.2mo1•L-1的KC1溶液

D．50m1、0.25mo1•L-1的NaC1溶液

答案

根据电离方程式，电离出的离子和溶质的量之间的关系来确定．

A、0.1mol•L-1的AlC13溶液中氯离子浓度是0.3mol/L；

B、0.1mo1•L-1的CaC12溶液中氯离子浓度是0.2mol/L；

C、0.2mo1•L-1的KC1溶液中氯离子浓度是0.2mol/L；

D、0.25mo1•L-1的NaC1溶液中氯离子浓度是0.25mol/L，

显然氯离子浓度最大的是0.3mol/L．

故选A．

完形填空

In the supermarket you would also find many frozen foods --- frozen fruits, vegetables, meat and fish. As techniques for 5.__________ (freeze) food are being improved, more frozen foods are appearing on the market, and more people are buying them. Fruits and vegetable to be sold in the supermarket are often frozen the moment 6._______are picked. The     7._________fruits and vegetable are frozen, the better.8._______machines are often taken into the fields where9.__________food grows, so that little time is lost 10.__________picking and freezing.
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多项选择题

一个文件对不同的用户可以具有读、写、执行权。如果希望对同组用户赋予全部权，请问下面的描述哪些是正确的：（）

A.chmod777文件名

B.chmod676文件名

C.chmod+x文件名

D.以上都不对
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