Deficient oxygen content inside a chain locker can be detected with（）.

A.that the vessel is anchored
B.to request the draw span of a bridge to be opened
C.of distress
D.that the vessel is broken down and drifting

A.have someone standing by
B.make sure there is sufficient air within the locker
C.de-energize the windlass
D.All of the above

A.of
B.to
C.for
D.on