單項(xiàng)選擇題

It is necessary to （） cool the various components of the machinery so that the engine can work properly.

A.continuously
B.regularly
C.constantly
D.period

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單項(xiàng)選擇題

It is necessary for us （） after having served for a certain period.

A.to change the lube oil
B.have the lube oil purified
C.have the lube oil burnt
D.to analyze the lube oil

單項(xiàng)選擇題

It is important to use only pure lead and to choose a thickness of wire which is greater than the normal allowable clearance but （） this amount.

A.not less than twice
B.greater at least twice than
C.not greater twice than
D.larger three times than

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