What is the purpose of the slip joint (splined connection) provided on the propeller shaft of a front-engine rear-wheel drive vehicle?

1. To allow angular movements of the propeller shaft as the axle moves.
2. To accommodate changes in the effective length of the propeller shaft due to suspension deflection.
3. To connect the gearbox output shaft directly to the clutch shaft.
4. To prevent the propeller shaft from whirling at high speeds.