单项选择题
A block that can be opened at the hook or shackle end to receive a bight of the line is a（）.
A.bight block B.gin block C.heel block D.snatch block
单项选择题 A buoy having red and green horizontal bands would have a light characteristic of（）.
单项选择题 A cabinet or space containing the controls or valves for the fixed firefighting system must be（）.
单项选择题 A carbon dioxide fire extinguisher should be recharged（）.
