使用压力钢瓶时，两瓶的间距和瓶与烧焊处的距离均应大于（）。
A．1m
B．2m
C．3m
D．4m
参考答案：C
Once a decision has been made, all of us should it. [ ]
A. direct
B. stick to
C. lead to
D. refer to
试述慢性脓胸的治疗。
