To determine if risk of collision exists，a vessel which is fitted with radar must use（）.

The shoreline along Rocky Point should give a good radar return because（）.

A.the shore is bluff and rocky
B.of offshore exposed rocks
C.submerged reefs cause prominent breakers
D.the lookout tower is marked with radar reflectors

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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

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