When performing a coupling test, you should pull against which part to verify the connection is secure?

Answer: A — Rear semitrailer's pin

During a coupling test, you’re checking that the kingpin is securely locked into the fifth wheel. Pull gently against the rear semitrailer’s pin (the kingpin) to see if the connection stays locked under load. If there’s any movement or the trailer separates, the kingpin isn’t properly secured. The electrical connector and landing gear aren’t what proves the coupling is secure, since they don’t carry the towing load. The latch being engaged matters, but the true test of a secure connection is that the kingpin remains locked when you apply a light pull.