A.3％～5％ B.5％～7％ C.7％～10％ D.10％～14％
A.20 B.15 C.10 D.5
A.氧气 B.氯气 C.氮气
A.7 B.10 C.15
A.4.5 B.3.5 C.4 D.5
A.78 B.21 C.19 D.34
