汽油是石油炼制产品之一，是汽车的主要燃料．请回答：
①汽油充分燃烧的产物是二氧化碳和水，由此可推断汽油的组成元素一定含有______元素．
②以汽油为燃料的汽车尾气中含有一氧化碳、氮的氧化物等大气污染物．目前，减少汽车尾气污染的措施之一，是在汽油中加入适量的乙醇．乙醇完全燃烧的化学方程式为：______．
③下列能替代汽油的燃料中，燃烧产物最清洁的是______（填编号）
A．天然气；B．乙醇；C．氢气．
（1）反应前后元素的种类不变，生成物二氧化碳和水中的碳元素和氢元素来自汽油．故填：碳和氢．
（2）乙醇完全燃烧的化学方程式为：C2H5OH+3O2
2CO2+3H2O． 点燃 .
（3）天然气和乙醇燃烧都能生成二氧化碳，二氧化碳能够导致温室效应，氢气燃烧的生成物只有水，不污染环境．故填：C．
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| James's New Bicycle James shook his money box again. Nothing! He carefully 1 the coins that lay on the bed. $24.52 was all that he had. The bicycle he wanted was at least $90! 2 on earth was he going to get the 3 of the money? He knew that his friends all had bicycles. It was 4 to hang around with people when you were the only one without wheels. He thought about what he could do. There was no 5 asking his parents, for he knew they had no money to 6 . There was only one way to get money, and that was to 7 it. He would have to find a job. 8 who would hire him and what could he do? He decided to ask Mr. Clay for advice, who usually had 9 on most things. "Well, you can start right here," said Mr. Clay. "My windows need cleaning and my car needs washing." That was the 10 of James's odd-job (零工) business. For three months he worked every day after finishing his homework. He was amazed by the 11 of jobs that people found for him to do. He took dogs and babies for walks, cleared out cupboards, and mended books. He lost count of the 12 of cars he washed and windows he cleaned, but the 13 increased and he knew that he would soon have 14 for the bicycle he longed for. The day 15 came when James counted his money and found $94.32. He 16 no time and went down to the shop to pick up the bicycle he wanted. He rode 17 home, looking forward to showing his new bicycle to his friends. It had been hard 18 for the money, but James knew that he valued his bicycle far more 19 he had bought it with his own money. He had 20 what he thought was impossible, and that was worth even more than the bicycle. | ||||
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