A.低碳鋼無縫鋼管,水煤氣鍍鋅鋼管 B.水煤氣鍍鋅鋼管,無縫鋼管 C.無縫鋼管,水煤氣鍍鋅鋼管 D.直縫焊鋼管,低碳鋼無縫鋼管
A.空氣 B.天然氣 C.氮氣 D.水
A.1% B.2% C.3% D.4%