单项选择题
A.decrease only
B.increase only
C.decrease slightly then returned to original speed
D.increase slightly then returned to original speed
单项选择题 The arrangement and shape of the cams on a diesel engine camshaft directly control which of the listed groups of operating conditions?（）
单项选择题 Corrosion inhibitors and/or soluble oils are added to diesel engine cooling systems to （）
单项选择题 Fuel droplets injected into a diesel engine cylinder must have adequate penetration to （）