摘要：有甲.乙.丙.丁四瓶无色气体.已知它们是氧气.空气.氢气和二氧化碳.为了 鉴别它们.下列方法中最方便的是······································································· ( ) A.观察颜色 B．分别倒入澄清的石灰水 C.把燃着的木条分别伸入四瓶气体 D．分别放入一只小白鼠

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