请将下列物质的有关知识按照一定的要求从大到小排列
（1）在水中的溶解性：a．氧气 b．一氧化碳 c．二氧化碳______；
（2）溶液的pH：a．蔗糖溶液 b．肥皂水 c．食醋______；
（3）有X、Y、Z三种金属，已知Y能从X的硫酸盐溶液中置换出X，Z能从Y的硝酸盐溶液中置换出Y，则X、Y、Z三种金属的活动性由强至弱的顺序是______．
（1）二氧化碳、氧气、一氧化碳在水中的溶解能力从大到小的顺序为：cab．故填：cab．
（2）肥皂水显碱性，pH大于7，蔗糖溶液显中性，pH等于7，食醋显酸性，pH小于7，蔗糖溶液、肥皂水、食醋等物质的pH由大到小的顺序为：bac．故填：bac．
（3）Y能从X的硫酸盐溶液中置换出X，说明Y的活动性比X强，Z能从Y的硝酸盐溶液中置换出Y，说明Z的活动性比Y强．X、Y、Z三种金属的活动性由强至弱的顺序是Z＞Y＞X．故填：ZYX．
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| Many people like to keep dogs as their pets. But do you know dogs were wild (野生的) animals long, long ago? The 1 wild dogs were trained by 2 in Europe about 10,000 years ago. These first "dogs" were not like 3 we have now. They may have been small wolves. These dogs often came near humans to 4 some food. Some of the young dogs were adopted (收养) by people and grew up with them. Humans believed the 5 were a help to them in many ways. The dogs helped them to hunt (狩猎). They could smell and hear danger 6 . people could. They helped keep people 7 on cold nights. So is was 8 to raise the dogs. Now, there are many different kinds of dogs 9 they may look quite different from each other. Dog trainers think there are more that 400 different kinds in the world. The number keeps increasing with new kinds. Since those early days, humans and dogs have always been together. We should 10 them from now on because they are really our friends. | ||||
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