Black smoke exhausting from an operating diesel engine is an indication of poor combustion which may be caused by （）

A.increased horsepower
B.reduced efficiency
C.increased heat loss
D.lower cylinder pressures

A.dangerous over-speeding
B.a loss of lube oil pressure
C.activation of the fixed CO₂ system for the emergency generator space
D.all of the above

A.provide energy to operate the engine between power impulses
B.neutralize the primary inertia force of the crankshaft
C.reduce the shock of starting loads on the main bearings
D.prevent the engine from operating at critical speed