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2009年，“神七”载着三名宇航员在太空来去自如，表明我国载人航天技术有了重大突破；运送火箭使用的燃料是偏二甲肼（化学式为C₂H₈N₂），下列说法正确的是（ ）

{C——12、H——1、N——14}

A. 偏二甲肼是碳、氢、氧三种元素组成的 B. 偏二甲肼中含有氮气

C. 偏二甲肼的相对原子质量是27

D. 偏二甲肼中碳、氢、氧三种元素的质量比为1：4：1