单项选择题
Back-up wires on a towed vessel provide（）.
A.a factor of safety B.additional strength C.a distribution of the towing load D.All of the above
单项选择题 At the instant when a string of casing being run from a ship is landed in the well head,（）.
单项选择题 Anchor shackles should have a breaking strength that is（）.
单项选择题 An anchor winch should be equipped with mechanical brakes capable of holding（）.
