The correct answer is B) The inertia of the turbocharger rotor causes a time lag which delays the turbocharger speed increase. When an excessive additional load is applied too quickly to a turbocharged diesel engine, the inertia of the turbocharger rotor causes a delay in the turbocharger's ability to spin up and provide the necessary boost pressure. This delay results in an air-fuel ratio that is too rich, leading to incomplete combustion and the production of black smoke from the exhaust. The other answer choices are incorrect because they do not accurately explain the primary reason for the black smoke under these conditions. Excessive exhaust energy would actually draw more air, and exhaust gas pumping losses or back pressure changes would not be the direct cause of the black smoke in this scenario.