单项选择题
A.the piston rods B.the crank throws C.the thrust bearings D.the main bearings
All three systems have the ports （） to swirl the incomi...
单项选择题All three systems have the ports （） to swirl the incoming air and direct it in the appropriate path.
A.angled B.rounded C.being angled D.being rounded
All the rings are slightly rounded on their external to...
单项选择题All the rings are slightly rounded on their external top and bottom edges to keep the oil film on the cylinder liner during （） for new piston rings.
A.the running-in period B.the running process C.gas exchange process D.the boiler firing
Air cocks, usually positioned at the （） in a circulatin...
单项选择题Air cocks, usually positioned at the （） in a circulating system, is used to get rid of the air in the system.
A.bending joint B.expansion tank C.weld D.the highest point
