Final answer:
When it starts to rain, the first thing you should do (besides turning on windshield wipers) is slow down and increase your following distance.
Step-by-step explanation:
When it starts to rain, the first thing you should do (besides turning on windshield wipers) is slow down and increase your following distance (option b). This is because wet road surfaces reduce traction and can cause your tires to lose grip. By slowing down and increasing your following distance, you give yourself more time to react and prevent skidding or hydroplaning.