A. 氧气瓶、乙炔瓶必须垂直放置 B. 回火时应先关乙炔阀,再关氧气瓶 C. 不可用铁丝捆扎焊枪胶管口
A. Yes, but the faces should be recognizable B. Yes, but the fans must be obedient. C. Yes, but the number must be limited D. Yes, but they must be checked
A. (1)+(2)+(3) B. (1)+(3) C. (2)+(3)