What causes diesel fuel to be ignited in the cylinder of an operating diesel engine?（）

A.seal the space between the piston and the liner
B.reduce the amount of lube oil burned in the combustion chamber
C.transmit heat from the piston to the cylinder liner
D.damp out fluctuations of the piston side thrust

A.when the engine RPM is pulled down by overload
B.at rated engine RPM
C.at 95 % of rated engine RPM
D.at 95 % of a properly adjusted governor RPM with the engine under full load