单项选择题
An oxygen indicator can be used to determine if there is（）.
A.sufficient oxygen in a compartment to support life B.combustible gases present C.hydrogen gas present D.All of the above
单项选择题 An on-load release system on a survival craft means the cable can be released（）.
单项选择题 An effective braking system for windlasses on rigs in deep water is a(n)（）.
单项选择题 A wooden plug fitted tightly in the vent of a damaged tank may prevent the tank from（）.
