单项选择题
A.keeps sparks from falling into an open tank
B.secures covers on ullage openings
C.prevents sparks from getting out of an engine's exhaust system
D.grounds static electricity
单项选择题 A single fitting installed in a pipeline that either blanks off the pipe or allows a full flow passage of a liquid through the pipe is referred to as a（）.
单项选择题 A ship crane which has been idle for a period of over six months shall be inspected to the same standards as a（）.
单项选择题 A sheepshank is used to（）.