单项选择题
To determine if risk of collision exists，a vessel which is fitted with radar must use（）.
A.radar scanning B.radar plotting C.compass bearings D.All of the above
单项选择题 The shoreline along Rocky Point should give a good radar return because（）.
单项选择题 The radio waves used for radar are very short，only（）long.
单项选择题 The radar control used to reduce sea return at close ranges is the（）.
