Final answer:
A) Brake fluid. Brake fluid should never be installed in a manual transmission. It can lead to severe damage and malfunction of the transmission components.
Step-by-step explanation:
The fluid that should never be installed in a manual transmission is brake fluid. Brake fluid is specifically designed for hydraulic braking systems and is not suitable for use in a transmission. If brake fluid is added to a manual transmission, it can lead to severe damage and malfunction of the transmission components. It is important to use the correct type of fluid, which is gear oil or transmission fluid, based on the manufacturer's recommendations for the specific make and model of the vehicle.