單項(xiàng)選擇題

To obtain accuracy in fixing by DF，（）and three stations should be used.

A.parallel bearings
B.long-range bearings
C.short-range bearings
D.cross bearings

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單項(xiàng)選擇題

Vessels in port may use（）for receiving typhoon warnings during the typhoon season.

A.their transmitters
B.their receivers
C.their radars
D.their lorans

單項(xiàng)選擇題

We’ll see（）the compasses are in good condition.

A.if
B.how
C.when
D.where