A converter dolly is:
Correct. A converter dolly has a small frame, axle(s), and a fifth wheel mounted on top — it transforms a semi-trailer into a full trailer behind another trailer.
CDL Practice Question #345
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.