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單項(xiàng)選擇題

On what type of pump would you find an impeller?（）

A.Centrifugal
B.Gear
C.Piston
D.Vane

單項(xiàng)選擇題

On navigational aids，what does the light characteristic Fl(2+1) mean?（）

A.A flashing light combined with a fixed light of greater brightness
B.Light flashes combined in groups，with a different number of flashes in each group
C.A light showing groups of two or more flashes at regular intervals
D.A fixed light varied at regular intervals by groups of two or more flashes of greater brightness