题干

甲、乙、丙三种物质之间的转化关系如右图,已知甲是常见的气体单质,乙、丙都只含两种元素,且组成元素相同。

回答下列问题:
(1)甲的名称是____ ,丙的化学式____ 甲的一种用途是____ 
(2)写出“丙→甲”反应文字表达式____,从微观角度看,该反应中没有改变的微粒是____(填符号)。

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答案(点此获取答案解析)

氧气,H2O,供给呼吸(支持燃烧等),水氢气+氧气​,H 、O

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    I have never forgotten the firm belief I had in the arrival through the chimney (烟囱) of the little Santa Claus (圣诞老人), the kind, white-bearded old man who at midnight left in my tiny shoe a present I found the next morning.

    Midnight! It's the perfect hour children don't know. What great efforts I made not to go to sleep before the little old man appeared!

    I had both a great desire and great fear of seeing him, but could never stay awake until then, and the next day my first look was for my shoe. He never failed to carefully wrap (包装) every present for me. I would run barefoot to get my treasure. It never was a very expensive present, for we were not rich. It was a cookie, an orange, or very simply a fine red apple. But it felt so precious that I barely dared to eat it. What a great role imagination plays in a child's life!

    I do not at all agree with the idea that the lies about Santa Claus should be stopped. Doubts and truth come all too soon on their own. I very well remember the first year, when I was five or six, I doubted that it was not Santa Claus who put the cookie in my shoe. Since then, it has never tasted as good as the first few years of my life.

    I noted that my son believed in him longer; boys are more naïve (天真的) than little girls. Like me, he made great efforts to stay awake until midnight. Like me, he loved the cookie baked in Heaven's kitchens. And like me, the first year of his doubts was the last year of the visit of the good old man.