A SEAMARK，I.E. A BUOY，INDICATING THE NORTH，EAST，SOUTH OR WEST FROM A FIXED POINT，E.G. A WRECK is（）.

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（）.

A.true north
B.magnetic north
C.the vessel's beam
D.the vessel's head

单项选择题A preferred-channel buoy will show a（）.

A.white light whose characteristic is Morse (A)
B.group-occulting white light
C.composite group-flashing (2 + 1) white light
D.composite group-flashing (2 + 1) red or green light

单项选择题A preferred-channel buoy may be（）.

A.lettered
B.spherical
C.showing a white light
D.All of the above

单项选择题A plane that cuts the Earth’s surface at any angle and passes through the center will always form（）.

A.the equator
B.a great circle
C.a small circle
D.a meridian