Final answer:
The proper time to slow down when approaching a curve is right before you enter the curve to ensure vehicle stability and prevent potential loss of traction that could occur if decelerating while in the curve.
Step-by-step explanation:
If a curve requires you to slow down, the correct time to do so is C) Right before you enter the curve. This is the safest approach because reducing speed while you are actually in the curve can cause loss of traction, which might lead to skidding or rollover, especially at high speeds. By slowing down before entering the curve, the vehicle is more stable and can smoothly navigate the turn. Additionally, rule of thumb for maintaining control in a curve is to: slow down, steer through the curve, and then accelerate once you're beginning to exit the curve.
Race car drivers, as mentioned in the context provided, also aim to take the inside path around a curve because it's the shortest route and allows them to maintain higher speeds safely. Such strategies illustrate the importance of proper speed and path selection to navigate curves effectively.