单项选择题
A.2.0%~7.4% B.2.5%~7.4% C.2.0%~8.4% D.2.5%~8.4%
A.氧气 B.氢气 C.氮气 D.水
A.调整副火嘴和风门 B.调整风门 C.慢慢打开燃料气阀 D.打开烟道挡板进行通风