Final answer:
To maintain a safe following distance and ensure enough cushion, the three-second rule should be used, not the rearview mirror, side mirrors, or vehicle's brake lights by themselves. This rule accounts for reaction and stopping distances under various road conditions.
Step-by-step explanation:
To determine if you have enough cushion between you and the vehicle you are following, none of the options given are correct by themselves. You should use the three-second rule as a guide to maintain a safe following distance. This helps account for the total distance your vehicle covers before you can react and stop. You should watch the vehicle ahead pass a fixed object and ensure it takes at least three seconds before your vehicle passes the same fixed point. Additionally, factors like road conditions and driver reaction time are important in determining adequate stopping distance. While mirrors and observing the vehicle's brake lights can help you be aware of your surroundings, they do not directly determine if the cushion is adequate.