如图是甲和乙在一定条件下反应前后分子种类变化的微观示意图。下列叙述正确的是（ ）
【分析】根据甲和乙在一定条件下反应前后分子种类变化的微观示意图写出方程式，根据物质的组成、方程式的意义、物质的性质和变化等分析判断有关的说法。
【解答】解：由图可知，该反应的方程式是：
A、氧化物是由氧元素和另一种元素组成的化合物，甲为一氧化碳，属于氧化物，丙为氮气，属于单质，故A错误；
B、由方程式的意义可知，反应生成的丙与丁的分子个数比为1：2，故B错误；
C、化学反应前后原子的数目不变，故C错误；
D、该反应的反应物均为有害气体，生成物均为无害气体，所以该反应能使有害气体转化为无害物质，故D正确。
故选：D。
【点评】解决这种题的关键就是辨别分子是由何种原子构成，每种原子有几个，这样就可以得出分子的化学式，写出方程式，在对相关知识进行分析判断即可。
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请在字典中查一下这个词。
我喜欢甜食， 你知道的。
去年， 彼得在旅途中和许多人交了朋友。
我叫托尼· 史密斯， 史密斯是我的姓。
我们在课上回答问题时应该起立
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