What is the primary purpose of the trailer hand brake?

Answer: B — To test trailer brakes only

The primary purpose of the trailer hand brake is to engage emergency brakes. This brake is designed to be used in situations where the regular braking system may fail or when the trailer becomes disconnected. The hand brake provides a mechanical means to secure the trailer, ensuring it doesn’t roll away or cause accidents. This brake is essential for safety, particularly when the vehicle is parked, on an incline, or in adverse conditions. While testing trailer brakes is also an important function, it is not the main purpose of the hand brake. Its main function lies in providing a reliable method for emergency situations involving the trailer's movement or stability.