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單項選擇題

（） neutralizes the acid conditions and（） cleanses the rings and grooves.

A.The detergency；the alkalinity
B.The alkalinity；the detergency
C.The inhabitant；the water
D.The additives；the distilled water

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單項選擇題

（） is usually driven by the engine camshaft and supplies pilot air to the cylinder air start valve.

A.An air receiver
B.An operating valve
C.An automatic valve
D.An air distributor

單項選擇題

（） is made of a boss with separated blades mounted into it.

A.A variable pitch propeller
B.A variable pitch nut
C.A fixed pitch parallel
D.A fixed pitch screw

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