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

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

单项选择题A special purpose buoy shall be（）.

A.lighted with a white light
B.striped black and red
C.lighted with a red light
D.yellow

单项选择题A special mark (yellow buoy)，if lighted，may exhibit which light rhythm?（）

A.Flashing
B.Morse A
C.Equal interval
D.Occulting