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A
Only check the tractor
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B
Perform a complete walk-around verifying all couplings are secure (fifth wheels locked, pintle hooks latched, safety chains connected), all air and electrical lines are correctly connected and not dragging, and test that all trailer brakes and lights work
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C
No final check is needed
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D
Only honk the horn
Why this is the answer
FINAL CHECK AFTER COUPLING DOUBLES: Before driving a newly coupled set, perform a thorough walk-around verification: ALL COUPLINGS SECURE: Tractor fifth wheel locked on the first trailer's kingpin (tug test + visual); dolly's fifth wheel locked on the rear trailer's kingpin; pintle hook latched and locked around the dolly tow bar eye; safety chains connected; no gaps at any fifth wheel; AIR LINES: All glad hands connected correctly (service and emergency at each point), secured, not leaking, not dragging or tangled; ELECTRICAL: All connections made, all lights and signals working on all trailers; BRAKE TEST: Charge the system; verify all trailers' brakes apply and release properly; check for air leaks; LANDING GEAR/DOLLY: Fully raised/positioned; everything secured; WHY: The multiple connection points in doubles mean any one missed connection (a loose pintle hook, an unconnected air line, a high hitch) could cause a separation, brake failure, or lost lights while driving — catastrophic with multiple trailers; the final walk-around catches errors before they become highway emergencies; thorough verification of every coupling, air, and electrical connection is the essential final step and a defining responsibility of doubles/triples operation.
Source: FMCSA CDL Manual — Doubles/Triples, Final Coupling Check