单项选择题
A.1~2mmH20 B.2~3mmH20 C.3~4mmH20 D.5~6mmH20
A.10%~20% B.20%~30% C.30%~40% D.40%~100%
A.10%~20% B.20%~30% C.30%~40% D.40%~50%