The correct answer is C) continue through the afterburning period. In a diesel engine, fuel combustion should begin just before the piston reaches top dead center and continue through the afterburning period. This allows for complete combustion of the fuel, which maximizes engine efficiency and power output. The fuel injection should be timed to ensure the combustion process is ongoing as the piston reaches the top of its stroke, rather than ending abruptly at top dead center or continuing significantly past bottom dead center. The afterburning period allows any remaining fuel to be fully consumed, improving the engine's overall performance and fuel economy. The other answer choices are incorrect because A) ending fuel injection at the completion of fuel injection would cut off the combustion process prematurely, B) ending combustion at bottom dead center would be too late in the cycle, and D) completing combustion exactly at top dead center would be too precise and not account for the natural variation in the combustion process.