单项选择题
The official number of a documented vessel is（）.
A.not required to be anywhere on the vessel B.required to be permanently marked on the vessel's structure C.required to be painted on the vessel;s stern D.required to be painted on the vessel's bow
单项选择题 The original equilibrium position is stable when（）.
单项选择题 The remote control for a fixed fire extinguishing system should be（）.
单项选择题 The sign used to caution persons approaching the gangway of a tank barge during cargo transfer reads（）.
