When is it acceptable to overtake on the left?

Overtaking on the left is typically considered acceptable when the vehicle in front is indicating to turn right. This situation arises because the vehicle preparing to turn right will be slowing down or coming to a stop, creating an opportunity to safely pass on the left without causing interference. This maneuver allows traffic to flow smoothly, especially in scenarios where right-turning vehicles may disrupt the flow of vehicles behind them.

Options that suggest it's acceptable to overtake on the left under broader circumstances, such as when the road is clear and straight, do not take into account the general rule that overtaking should ideally be done on the right to maintain consistency and predictability on the roads. Therefore, while the clear road scenario might seem tempting, it does not align with the fundamental principles of road safety and traffic laws that are designed to minimize confusion among drivers.

Additionally, overtaking should always be approached with caution and consideration for traffic laws and the behavior of other drivers. Thus, while overtaking on the left can be appropriate in the specific case of a right-turning signal, it is generally advised against in other situations, making choice B the most suitable answer.