The quickest way to stop is to

Answer: C — Apply both brakes at the same time.

Applying both brakes at the same time is the quickest way to stop because it helps distribute the braking force between the front and rear tires, providing more stability and control. B and D should be avoided because applying only the front or rear brake can cause skidding or loss of control. A rider should also avoid downshifting instead of braking as it requires more time and distance to slow down the motorcycle.