Which of the following indicates that a driver may be distracted?

The option indicating that the vehicle cannot keep a constant speed is a clear sign of potential driver distraction. When a driver is distracted, their attention may wander away from the task of driving, leading to difficulties in maintaining control of the vehicle. This can manifest in varied acceleration and deceleration, causing the vehicle to fluctuate in speed. This constant change in speed could be related to the driver’s lack of focus, as they might be trying to manage other tasks or responding to distractions instead of concentrating fully on the road.

The other options do not necessarily link as directly to distraction behavior. Frequently changing lanes might indicate aggressive driving or uncertainty, while driving with one hand is not inherently indicative of distraction — many experienced drivers can do this safely under certain conditions. Having headlights on could be a normal safety measure, depending on the weather or time of day, rather than a sign of distraction. Therefore, the inability to maintain a constant speed is most indicative of distraction in the driving context.