What constitutes an unlawful action while driving a CMV related to a violation?

Answer: B — Driving with a revoked CDL

Driving with a revoked Commercial Driver's License (CDL) is indeed considered an unlawful action while operating a Commercial Motor Vehicle (CMV). A revoked CDL indicates that the driver has lost their eligibility to operate a CMV, often due to prior violations or infractions, and is not legally permitted to drive until the revocation has been lifted. In the context of CMV regulations, ensuring that drivers hold valid licenses is crucial for maintaining safety on the roads. This rule serves to protect both the driver and the public by ensuring that only those who adhere to safety and regulatory standards are allowed to operate these large and potentially dangerous vehicles. By contrast, the other options either pertain to minor infractions that may not directly and significantly compromise driving safety (like failing to signal or driving under the speed limit) or involve having a valid license. Hence, those actions do not meet the same threshold for unlawfulness as driving with a revoked CDL.