D. Checking to see if the brake fluid is contaminated.
Explanation:
In this picture, the owner of the car is checking to see if the brake fluid is contaminated. The brake fluid is in charge of transferring pedal break pressure and movement to the brake assemblies. One of the most important tasks that the fluid performs is lubrication. However, if the fluid wears out or is contaminated, its properties can be reduced. This is why it is important to periodically check this fluid.
