单项选择题
A.increase back pressure during the exhaust process
B.facilitate periodic replacement of the valves
C.reduce the pumping loss associated with scavenging
D.reduce tension on valve springs
单项选择题 If the compression rings on a diesel engine piston become stuck in the ring groove, the cause may be due to（）
单项选择题 Diesel engine electric starting motors generally require heavier duty motors and motors and operate at higher voltages than comparable starting motors for gasoline engines due to（）
单项选择题 The size of the exhaust valve opening is （）