What should you be cautious of when you encounter a slippery when wet sign?

The correct choice emphasizes the need for adjusting your speed in response to potentially slick conditions. When you see a slippery when wet sign, it serves as a warning that the road may not provide the usual level of traction, especially in adverse weather conditions such as rain or snow.

Reducing your speed allows for better control of your vehicle, increasing your reaction time, and providing a greater margin for safety should you encounter unexpected obstacles or difficulties in handling your vehicle on slippery surfaces. It's vital to drive at a speed that allows you to maintain control and stop safely if necessary, which may be significantly slower than your normal driving speed under dry conditions.

Other options, such as increasing speed or maintaining normal speed, contradict the principle of driving safely in adverse weather – which requires more cautious handling of your vehicle. Driving with headlights off not only reduces visibility for yourself but also for others on the road, which is not appropriate when road conditions are hazardous.