单项选择题
A petroleum liquid has a flash point of 85°F. This is a grade （）.
A.B flammable liquid B.C flammable liquid C.D combustible liquid D.E combustible liquid
单项选择题 A negative metacentric height （）.
单项选择题 A navigator fixing a vessel’s position by radar （）.
单项选择题 A natural fiber rope can be ruined by dampness because it may （）.
