The best way to stop quickly is to:

Answer: D — Use both brakes simultaneously.

Using both brakes simultaneously is the safest and most effective way to stop quickly on a motorcycle. This technique allows for a more controlled deceleration and helps distribute the stopping power evenly between both the front and rear brakes. The front brake provides most of the stopping power, due to the weight shift that occurs when you brake. By engaging both brakes, you maximize your stopping force and reduce the likelihood of skidding or losing control. It's important to note that the front brake alone can cause the rider to tip forward if used too aggressively, potentially leading to a loss of control. Conversely, relying solely on the rear brake may result in insufficient stopping power, especially in emergency situations. Therefore, using both brakes not only allows for a quicker stop but also helps maintain stability and balance, which is crucial for safe riding.