A.氧浓度25%~30%,氧流量1~2升/分,间断给氧B.氧浓度25%~30%,氧流量1~2升/分,持续给氧C.氧浓度35%~40%,氧流量2~3升/分,持续给氧D.氧浓度40%~55%,氧流量3~4升/分,持续给氧