单项选择题
A self-contained breathing apparatus is used to（）.
A.make underwater repairs to barges B.determine if the air in a tank is safe for men C.enter areas that may contain dangerous fumes or lack oxygen D.resuacitate an unconscious person
单项选择题 A set of interior steps on a ship leading up a deck from below is known as（）.
单项选择题 A sheave is a（）.
单项选择题 A smooth, tapered pin, usually of wood, used to open up the strands of a rope for splicing is called a (n)（）.
