The correct method of switching off a marine radar is to turn power switch to（）position first，then to（）position.

A.keeping a close watch and lookout
B.taking a radar range and bearing
C.observing a radar target and listening to signals
D.keeping a well clear caution

A.immediately when the contact is noted on radar
B.only if the radar scope is watched constantly
C.after the contact has been marked at least twice
D.by an occasional glance at the radar

A.the radar reflectors reflect better signals
B.fog horn signals travel farther to sea
C.it is equipped with strobe lights
D.it has a reduced watch circle