Final answer:
The purpose of applying the emergency brakes from the added cars is to check that the brakes are working properly.
Step-by-step explanation:
The correct answer is 1) the brakes are working properly. When cars are added to a train at a terminal, it is important to check that the brakes are functioning correctly. Applying the brakes in emergency from the added cars allows for testing and ensuring that the brakes are in proper working order before the train departs.