Braking distance is:

a. the distance your vehicle will travel (in ideal conditions), while you are braking.

b. the distance you will continue to travel (in ideal conditions), before you physically hit the brakes, in response to a hazard seen ahead.

c. the total minimum distance a vehicle has traveled under ideal conditions to bring your vehicle to a complete stop.

d. the distance your vehicle travels (in ideal conditions) from the time your eyes see a hazard until your brain recognizes it

a. the distance your vehicle will travel (in ideal conditions), while you are braking.

Explanation:

Perception Distance is how far your vehicle travels from the time your eyes see an obstacle until your brain recognizes it.

Reaction Distance is defined as how far you will continue to travel after seeing the obstacle until you physically hit the brakes.

Braking Distance is defined as how far your vehicle will travel while you are braking (applying brakes).

Total Stopping Distance is the total minimum distance your vehicle will travel that is including perception distance, reaction distance, and braking distance until you can bring your vehicle to a complete stop.