On a highway where there is a sign with the words "ONE WAY" and an arrow, you may:

The best understanding of the situation involves recognizing the significance of a "ONE WAY" sign with an arrow. This sign indicates that traffic is only permitted to move in the direction indicated by the arrow. Therefore, the correct answer aligns with the rule that states drivers must adhere strictly to the directional guidance provided by such signs.

Driving only in the direction which the arrow points ensures that all vehicles travel in a safe, organized manner, reducing the potential for collisions and confusion on the roadway. This adherence helps maintain smooth traffic flow and enhances safety for all road users.

In terms of the other answers, backing your car in the direction opposite the arrow would contravene the laws of safe driving as stipulated by the sign. Proceeding against the arrow, even if on part of the highway, would also contradict the established traffic regulations that prioritize safety and order. Driving solely on the right-hand side isn't specifically relevant in the context of a "ONE WAY" scenario as it doesn't ensure compliance with the directional restriction. Understanding and following the "ONE WAY" sign ensures that drivers remain within the boundaries of the law and maintain a safe driving environment.