单项选择题
A.submerged rock，not dangerous to navigation B.sunken wreck，not dangerous to navigation C.towed-under buoy D.All of the above
A vessel is（）when she is not at anchor，made fast to the...
单项选择题A vessel is（）when she is not at anchor，made fast to the shore，or aground.
A.underway B.making way C.dead in the water D.a power driven vessel
A structure，usually made of stone，or cement pilings，whi...
单项选择题A structure，usually made of stone，or cement pilings，which extends from the bank at approximately right angles to the current is called a（）.
A.dike B.revetment C.cutoff D.crib
A spherical buoy may be（）.A.numberedB.letteredC.greenD....
单项选择题A spherical buoy may be（）.
A.numbered B.lettered C.green D.red
