When the normal compression ratio of a diesel engine is not very high, misfiring at light loads may be caused by （）

A.exhaust manifold
B.valve bridge
C.pressure of the fresh air charge
D.valve adjusting gear

A.excessive compression pressure
B.air in the fuel lines
C.high fuel pressure
D.excessive load

A.reduce lube oil temperature
B.raise exhaust temperature reduce
C.excessive heating of engine room
D.reduce load on cooling water pump