vehicle with power assist brakes has a hard brake pedal with topping power.Which of these is the MOST likely cause of this condition? A. The brake booster. B. The master cylinder. C. Air in the system. D. Contaminated brake fluid.

## Step 1<br />The problem presents a situation where a vehicle with power assist brakes experiences a hard brake pedal with topping power. The task is to identify the most likely cause of this condition from the given options.<br /><br />## Step 2<br />The options provided are: A. The brake booster, B. The master cylinder, C. Air in the system, and D. Contaminated brake fluid.<br /><br />## Step 3<br />The brake booster is a component in the power brake system that uses engine power to assist braking. If the brake booster fails, it can cause a hard brake pedal with topping power.<br /><br />## Step 4<br />The master cylinder, air in the system, and contaminated brake fluid can also cause issues with the brake system, but they are less likely to cause the specific condition described in the problem.