What part does NOT rotate when the engine is running and the clutch is depressed?

When the clutch is depressed, the input shaft does not rotate. This is because the clutch disengages the engine from the transmission, allowing the driver to change gears without the input shaft being affected by the engine's rotation.

The clutch operates by separating the clutch plate from the flywheel, which is attached to the engine. When the clutch pedal is pressed, the pressure plate releases its grip on the clutch plate, which in turn decouples it from the flywheel. This action effectively breaks the connection between the engine and transmission, stopping the input shaft from spinning.

Meanwhile, the flywheel and pressure plate are still connected to the engine and may continue to rotate since they are directly tied to its operation. The clutch plate, when disengaged, also does not rotate with the input shaft. Thus, the key factor here is the state of the input shaft during the operation of the clutch, making it the part that does not rotate when the clutch is fully depressed.