单项选择题
A.scar B.scale C.spur D.bilge
It is necessary to （） cool the various components of th...
单项选择题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
It is necessary for us （） after having served for a cer...
单项选择题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
It is important to use only pure lead and to choose a t...
单项选择题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
