Because the couplings have mass the net force of tension on the train is the sum of the forces of the tension, therefore as you approach the end of the train there is greater tension so the answer is B. Least between the locomotive and the first car.

the tension is the most between the accelerating car and the first car because the engine is accelerating the whole train and there is the most tension between the engine car and the first car since the whole train acts as one mass. Further along the train cars there is a pull but not of the equal tension as the first car.