An efficient seal between the cylinder block and cylinder heads on many diesel engines is obtained with（）

A.Decrease the air density
B.Increase the exhaust temperature
C.Decrease the lube oil temperature
D.Increase the air density

A.Clogged oil pump suction screens
B.Increased oil operating temperatures
C.Sticking piston rings
D.All of the above

A.improper fuel rack positing
B.lengthy exhaust valve duration
C.extend operation at light load
D.excessively early injection timing