Final answer:
To ensure brakes are functioning normally, they should be tested once a month by driving the car at a reasonable speed and applying the brakes. This will help identify any potential issues or malfunctions before they become major problems.
Step-by-step explanation:
In order to ensure brakes are functioning normally, it is important to test them regularly. The correct answer to the question is option D) Once a month. Testing the brakes once a month will help identify any potential issues or malfunctions before they become major problems. This can be done by driving the car at a reasonable speed and applying the brakes to check for any abnormal noises, vibrations, or delays in stopping.