单项选择题
A.principle B.principal C.cause D.case
These piston rings are so badly worn that they must be ...
单项选择题These piston rings are so badly worn that they must be （）.
A.renewed B.welded C.machined D.chromium-plated
There should be a lubricating oil （） between the main b...
单项选择题There should be a lubricating oil （） between the main beatings and the crankshaft.
A.film B.cap C.lacquer D.shell
There is an injection pump for each cylinder, which is ...
单项选择题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
