单项选择题
Vessels must （） pilot at waiting anchorage．
A.wait B.wait for C.be waited D.be waited for
单项选择题 There shall be two principal （） through the harbor for the passage of vessels of over 60 tons burden．
单项选择题 The transfer procedures for oil products are required to be posted （）.
单项选择题 The step of a pilot ladder which prevents the ladder from twisting is the （）.
