单项选择题
The radio waves used for radar are very short，only（）long.
A.a few centimeters B.a few fathoms C.a few meters D.a few feet
单项选择题 The radar control used to reduce sea return at close ranges is the（）.
单项选择题 The radar control that shortens all echoes on the display and reduces clutter caused by rain or snow is the（）.
单项选择题 The radar control that reduces weak echoes out to a limited distance from the ship is the（）.
