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 spherical buoy may be（）.

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

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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

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