单项选择题
A chock（）.
A.is a deck fitting used to shackle gear to the deck B.permits easy jettisioning of deck cargo in an emergency C.prevents stress concentration in the bulwark D.provides opening through the bulwark for mooring lines
单项选择题 A chock is a（）.
单项选择题 A C02 portable extinguisher is annually checked by（）.
单项选择题 A contra-guide is a type of（）.
