The correct answer is: A. Engine to engine.
A dead engine is a locomotive that is not in use and is being towed by another locomotive. It is attached to the rear of the train, next to the engine that is powering the train. This is done to provide additional power and to help the train to climb hills.
Option B is incorrect because the dead engine is not attached next to the engine. It is attached to the rear of the train.
Option C is incorrect because the dead engine is not attached to both the engine and the rear of the train. It is only attached to the rear of the train.
Option D is incorrect because the dead engine is attached to the train.