A "doubles" combination uses a tractor plus:
Correct. Doubles = tractor + lead semi-trailer + converter dolly + second semi-trailer (which becomes a full trailer once on the dolly).
CDL Practice Question #382
Category: Doubles/Triples
Why this question matters
This question is one of 50 in our Doubles/Triples bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.