单项选择题
A.To receive the high-frequency pulses from the transmitter
B.To focus the pulses into a beam，and send them into space
C.To pick up reflected pulses coming from objects that have been struck by the beam
D.To reflect microwaves
单项选择题 You are using a radar in which your own ship is shown at the center，and the heading flash always points to 0°. If bearings are measured in relation to the flash，what type of bearings are produced? （）
单项选择题 You are underway in thick fog. You have not determined if risk of collision exists. Which statement is TRUE?（）.
单项选择题 You are underway in restricted visibility and hear a fog signal forward of the beam. Nothing appears on your radar screen. You must（）.