The correct answer is B) Late fuel injection. White exhaust smoke from a diesel engine typically indicates incomplete combustion, which is often caused by late fuel injection. When fuel injection is delayed, the fuel does not have enough time to fully combust, resulting in unburnt fuel being expelled as white smoke. This is in contrast to the other options, which would not directly lead to white smoke - excess air (A), excessive lube oil (C), or high compression temperature (D) would produce different exhaust characteristics.