单项选择题
A.gases B.paints C.inhibitors D.detergent
This used piston had been tested and approved as a spar...
单项选择题This used piston had been tested and approved as a spare part by the （） during last annual repair.
A.agent B.shipchandler C.surveyor D.engineer
They understand the （） of automatic sludge discharging ...
单项选择题They understand the （） of automatic sludge discharging of the purifierBut they are not good in practice.
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
