单项选择题
A gas-free certificate would usually be issued by a(n)（）.
A.CCS marine surveyor B.certified marine chemist C.port engineer D.MSA marine inspector
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（）.
单项选择题 On a hydrocarbon flammability chart the line which extends from 0% to 21.8% oxygen，lying tangent to the flammability range，is called the（）.
