单项选择题
A portable foam (stored-pressure type) fire extinguisher would be most useful in combating a fire in（）.
A.generators B.oil drums C.the bridge controls D.combustible metals
单项选择题 A portable dry chemical fire extinguisher discharges by（）.
单项选择题 A passenger vessel is required to have a supervised patrol when（）.
单项选择题 A marine chemist issues gas free certificates and is certified by the（）.
