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單項(xiàng)選擇題

（）by an ice-breaker, it is important to maintain a continuous listening watch on the appropriate VHF channel and to maintain a proper look-out for sound and visual signals.

A.which is assisted
B.that assist you
C.when you assisted
D.when being assisting

單項(xiàng)選擇題

The advantage of geostationary satellites is（）.

A.the range of antenna can cover everywhere in the world
B.we can know the ship’s exact position
C.that the distress alert can be located as soon as possible
D.antenna of permanent earth stations may be directed towards fixed points in the sky