單項(xiàng)選擇題

These piston rings are so badly worn that they must be （）.

A.renewed
B.welded
C.machined
D.chromium-plated

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單項(xiàng)選擇題

There should be a lubricating oil （） between the main beatings and the crankshaft.

A.film
B.cap
C.lacquer
D.shell

單項(xiàng)選擇題

There is an injection pump for each cylinder, which is usually operated once every cycle by （） on the camshaft.

A.a gear
B.a cam
C.a rod
D.a miler