Which of the following could suggest that a driver is not fully attentive?

A driver who is constantly changing speeds unnecessarily might be indicative of a lack of attentiveness because this behavior can suggest that the driver is not maintaining a consistent awareness of their surroundings and the flow of traffic. Consistent speed is an essential aspect of safe driving, as it helps to ensure that the driver is in harmony with other vehicles on the road. When a driver fluctuates speed without reason—such as changes that do not correlate with road conditions, traffic signals, or the movement of other vehicles—it can create confusion for other drivers and increase the risk of accidents.

By contrast, behaviors like following traffic rules, checking mirrors regularly, and using turn signals appropriately demonstrate a driver's commitment to safety and attentiveness. These actions reflect a level of awareness that is crucial for effective driving, showing that the driver is actively engaged in monitoring their environment and communicating with other road users. Thus, consistently changing speeds without justification is a clear indication that a driver may not be fully attentive.