单项选择题
The pistons are cooled by oil supplied from the forced （） system.
A.fresh water B.sea water C.lubrication D.fuel oil
单项选择题 The piston supporting body is mainly subjected to （） stress.
单项选择题 The piston rings if found worn out （） and supplied by shipchandler.
单项选择题 The piston rings are manufactured with a diameter （） the bore of the cylinder.
