单项选择题
A relief valve for a cargo pump is generally installed（）.
A.after the discharge valve B.between the pump and discharge valve C.after the suction valve D.between the pump and suction valve
单项选择题 A gas-free certificate would usually be issued by a(n)（）.
单项选择题 A fire of escaping liquefied flammable gas is best extinguished by（）.
单项选择题 A chemical additive to LPG gives it a characteristic（）.
