When is it acceptable to travel in the left lane of a highway?

Traveling in the left lane of a highway is generally intended for specific purposes to promote safety and efficient traffic flow. The correct option highlights two main scenarios where it's appropriate to use the left lane: when overtaking another vehicle or preparing to make a left turn.

When overtaking, driving in the left lane allows faster-moving vehicles to pass those that are traveling more slowly. This is crucial because it helps maintain the flow of traffic and reduces the likelihood of congestion or accidents that can occur when faster vehicles are stuck behind slower ones. Additionally, using the left lane for a left turn is necessary as it positions the vehicle for safely executing the maneuver.

In contrast, leisurely driving, personal preference, and slow-moving traffic are not valid reasons to occupy the left lane. Doing so can obstruct faster-moving traffic and create hazards on the road. Therefore, adhering to the guidelines of using the left lane for overtaking or preparing to turn helps keep highways safer and more efficient for all drivers.