单项选择题
A rock and sand structure extending from the bank of the river toward the channel is known as a（）.
A.wingdam B.towhead C.cutoff D.landwall
单项选择题 A relative bearing is always measured from（）.
单项选择题 A preferred-channel buoy will show a（）.
单项选择题 A preferred-channel buoy may be（）.
