What rule applies for maintaining a safe following distance in wet or frosty conditions?

Answer: D — Four-second rule

In wet or frosty conditions, the four-second rule is the recommended approach for maintaining a safe following distance. This longer distance is crucial because wet or icy road surfaces reduce traction and increase stopping distances significantly. By allowing a four-second gap, riders provide themselves with adequate time and space to react to any sudden changes in traffic, allowing for a safe and controlled stop if necessary. The need for a longer following distance is due to the fact that wet and frosty conditions can lead to reduced visibility as well as decreased grip on the road, increasing the likelihood of skidding or losing control. By adhering to the four-second rule, riders can account for these hazardous conditions and enhance their safety while navigating through them.