Final answer:
To test a tractor-trailer hook-up, stop pulling against the locked trailer brakes when the tractor remains stationary for at least 5 seconds.
Step-by-step explanation:
When testing your tractor-trailer hook-up, you need to pull gently against the locked trailer brakes and stop when your tractor does not move for at least 5 seconds. The correct answer to the question is B. your tractor does not move for at least 5 seconds. It's important to ensure that the tractor and trailer are securely connected before initiating movement, which is confirmed by a static test like the one described. Performing checks like these are critical for safety on the road as they ensure that the connection between the tractor and trailer can withstand the forces of driving without separating.