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.numberedB.letteredC.greenD....

单项选择题A spherical buoy may be（）.

A special purpose buoy shall be（）.A.lighted with a whit...

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

A special mark (yellow buoy)，if lighted，may exhibit whi...

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