单项选择题
One of the factors which affects the circulation of ocean currents is（）.
A.humidity B.varying densities of water C.vessel traffic D.the jet stream
单项选择题 Vessels，（）support vessels，should not enter the safety zone of a deepwater port unless clearance has been obtained from the Vessel Traffic Supervisor.
单项选择题 The Rules state that vessels may depart from the Rules when（）.
单项选择题 Which statement about the Navigation Rules is TRUE?（）.
