单项选择题
A.氮气 B.空气 C.水蒸汽
A.大 B.小 C.相等 D.不一定
A.1.4%~7% B.1.4%~7.5% C.1.4%~8% D.1.4%~8.5%
A.1.2 B.1.4 C.1.5 D.2.5
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