A diesel engine experiences a sudden loss in speed, accompanied by black exhaust smoke, with the fuel rack at maximum, and the speed remaining below normal. The probable cause is __________.

Correct Answer: Option A — engine overload

When an engine is subjected to excessive external resistance or propeller binding, the resulting engine overload causes a rapid drop in speed. Despite maximum fuel rack position, unburned fuel creates heavy black smoke due to insufficient air-fuel ratios and incomplete combustion.