Which of the following is a disqualifying factor for a CDL?

Answer: B — DUI conviction within the last three years

A DUI conviction within the last three years is indeed a serious disqualifying factor for obtaining or retaining a Commercial Driver License (CDL). This is because commercial drivers are held to higher standards of safety due to the nature of their jobs, which often involve operating large and heavy vehicles. A DUI shows a violation of safe driving principles and indicates a risk to public safety, making it imperative that such convictions lead to disqualification from holding a CDL. Other factors such as a speeding ticket within the last year or driving without a license may not automatically disqualify someone from obtaining a CDL; instead, they could result in points being added to the driver's record or other penalties. Similarly, failing to pay tolls, while potentially affecting a driver's record and relationship with driving authorities, does not typically carry the same weight as a DUI conviction when it comes to disqualification.