Before backing the second trailer onto the converter dolly's fifth wheel, what should the driver check about the dolly?

COUPLING THE SECOND TRAILER TO THE DOLLY: Before backing the rear trailer onto the dolly's fifth wheel: POSITION/ALIGN: The dolly should be lined up with the trailer kingpin; FIFTH WHEEL READY: Jaws OPEN (unlocked) to receive the kingpin; properly greased; HEIGHT: The dolly's fifth wheel at the correct height relative to the trailer kingpin (so the kingpin enters the jaws properly — not too high or low); SECURE THE DOLLY: The dolly should be prevented from moving (chocked or braked) so it doesn't roll away when the trailer contacts it; SAFE PROCEDURE: Connect the dolly to the front trailer first (pintle hook, safety chains, air/electrical); then back the rear trailer onto the dolly's fifth wheel just like coupling a tractor to a trailer; VERIFY: After coupling, check the kingpin is locked in the jaws (jaws closed around the shank, no gap), do a tug test, and inspect; DOUBLES/TRIPLES coupling has multiple steps and connection points; each fifth wheel coupling requires the same verification as a tractor-trailer coupling; preparing the dolly correctly (open jaws, correct height, secured) is essential before backing the trailer onto it.