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