A white buoy with an open-faced orange diamond on it indicates（）.

单项选择题A white buoy with a blue band is（）.

A.an isolated danger mark
B.a hydrographic data collection buoy
C.a mooring buoy
D.marking a restricted area

单项选择题A V-shaped ripple with the point of the V pointing upstream in a river may indicate a（）.

A.submerged rock，not dangerous to navigation
B.sunken wreck，not dangerous to navigation
C.towed-under buoy
D.All of the above

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

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

单项选择题A spherical buoy may be（）.

A.numbered
B.lettered
C.green
D.red