A commercial vehicle driver is regarded as being on duty except when...?

Answer: B — Taking a lunch break between trips

When operating a commercial vehicle, the law considers the driver to be on duty at all times except for when they are taking a break between trips. Driving on the highway, refueling, and loading or unloading cargo are all considered part of the driver's duties and therefore they are considered to be on duty during these activities. Taking a lunch break between trips is the only exception where the driver is not considered to be on duty.