单项选择题
A.lime B.frost C.scale D.scar
It is necessary to remove （） from the cooling spaces.A....
单项选择题It is necessary to remove （） from the cooling spaces.
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
