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單項(xiàng)選擇題

As the propeller turns，voids are formed on the trailing and leading edges of the propeller blades causing a loss of propulsive efficiency，pitting of the blades，and vibration. These voids are known as（）.

A.advance
B.cavitation
C.edging
D.slip

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單項(xiàng)選擇題

As oil pipe line connections were broken，（）quantity of oil was caused to spill onto the wharf and into the dock water.

A.a not knowing
B.an unknowing
C.an unknown
D.a not known

單項(xiàng)選擇題

Anchors are prevented from running out when secured by the（）.

A.brake
B.devil's claw
C.pawls
D.All of the above

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