单项选择题 After an IOPP Certificate is issued to an inspected vessel，how many other surveys of the vessel’s pollution prevention equipment are conducted during the period of validity of the certificate?（）

单项选择题 A vessel is found to be seaworthy after a complaint in writing to the American Consul by the Chief and Second Mates. The cost of the survey is to be paid by the（）.

单项选择题 A vessel engaged in（）shall not impede the passage of any other vessel navigating within anarrow channel or fairway.