Explanation:

- Option 1: Perfectly inelastic

- At full employment, the Keynesian Aggregate Supply (AS) becomes vertical and perfectly inelastic, showing no additional output can be produced.

- Option 2: Perfectly elastic

- Before full employment, the Keynesian AS curve is typically horizontal. Firms can increase production without increasing prices due to idle resources and unemployment.

- Option 3: Unitary elastic

- This implies a proportionate change in output and price, not typical of the initial stages of the Keynesian AS curve.

- Option 4: More elastic

- Suggests something is elastic but not perfectly so, which doesn’t perfectly describe the Keynesian AS before full employment.