What should you do if you encounter a sign indicating a slippery road due to rain?

Answer: D — Reduce your speed and drive with caution.

When encountering a sign indicating a slippery road due to rain, it is important to reduce your speed and drive with caution. Increasing speed can make it harder to maintain control of the vehicle, while sudden braking can cause skidding. Steering in the opposite direction of a skid is also not recommended as it can be difficult to do correctly in a moment of panic. Reducing speed and being cautious will give you better control and allow you to slow down if needed.