Final answer:
The correct option is: C) both side gears and pinion gears. Friction modifiers are required for proper operation in both side gears and pinion gears in a differential. Without friction modifiers, the gears may experience excessive wear and the differential may not function properly.
Step-by-step explanation:
In a differential, friction modifiers are required for proper operation in both side gears and pinion gears. The purpose of friction modifiers is to reduce the friction between the gears, allowing them to rotate smoothly and efficiently. Without friction modifiers, the gears may experience excessive wear and the differential may not function properly.
The correct option is: C) both side gears and pinion gears. Friction modifiers are required for proper operation in both side gears and pinion gears in a differential. Without friction modifiers, the gears may experience excessive wear and the differential may not function properly.