用一种试剂及相关操作就可除去下列物质中的杂质（括号内为杂质），写出该试剂的化学式（试剂是溶液的，仅需写出溶质的化学式）：
（1）CaC12（CaO）______（2）KNO3（NaCl）______（3）NaOH（Na2CO3）______．
（1）氧化钙与盐酸反应生成氯化钙，故答案为：HCl，
（2）硝酸钾的溶解度受温度的变化影响较大，而氯化钠的溶解度受温度影响变化较小，将混合物配成热的饱和溶液，然后冷却热饱和溶液，就可以提纯硝酸钾，故答案为：H2O，
（3）碳酸钠和氢氧化钙反应生成氢氧化钠和碳酸钙沉淀，过滤将碳酸钙沉淀除去，就剩下氢氧化钠了，故答案为：Ca（OH）2．
完形填空（共20小题；每小题1.5分，满分30分） 阅读下面短文，从短文后各题所给的四个选项（A、B、C和D）中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。 When I met Mr Jim Lemon I was a seventeen-year-old freshman at Houston's Jackson Junior High.The chances of my finishing high school were 36 . I was a troubled teenage. Mr Lemon taught American history and was quite 37 from the other teachers I had known. Not only was he 38 , but also he was a great teacher. He pushed and never tolerated the mediocrity(平庸) that had become my standard. On the occasion of our first semester report cards, Mr Lemon 39 me aside and asked how it was possible that I was a B student in his class and a C student in the 40 of my classes. I passionately told him about my 41 parents, the local gangs, the drugs, the fights, the police---all of the evils I had been 42 to. It was then that Mr Lemon 43 explained that the only person 44 for my situation was me. And the only person with the 45 to change my situation was me. He 46 me that I was failing not because I was a failure. He inspired me to become a better student and he 47 my life. Ten years later I was preparing to graduate from a university when I spoke to him again . 48 I did get him on the phone, I told him that I had been saving money so that I could invite him to come to Hawaii at my 49 to be a part of my graduation. I'll never forget his 50 . He said,"Who is this again?" I was just one of hundreds of the students whose life he changed 51 he had no idea of his influence. Mr Lemon never came to my graduation, but his 52 taught me another valuable lesson. His final lesson for me was that we will never know or understand the 53 we have on other people's lives. He taught me that we all have the 54 to effect people's lives for the 55 ... Or for the worse.
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