Final answer:
The FMCSA only allows answering a hands-free cell phone by touching a single button while driving a CMV to reduce distractions and improve road safety.
Step-by-step explanation:
According to the Federal Motor Carrier Safety Administration (FMCSA), the permissible action while driving a Commercial Motor Vehicle (CMV) is C. Answering a hands-free cell-phone by touching a single button. This is allowed because it minimizes the driver's distraction and allows for better focus on the road. Holding a cell phone in one hand (A), reaching for a phone to check a message (B), and dialing a phone number while at an intersection (D) are actions that are generally prohibited under FMCSA rules as they can lead to significant distractions and increase the risk of accidents.