Movements along AS curve from variable cost changes

Steps:

• Identify that aggregate supply (AS) curve shows total output supplied at different price levels.
• Distinguish movement along (change in quantity supplied due to price level or related costs) from shifts (changes in curve position from external factors).
• Evaluate each option: check if it alters quantity supplied without shifting the entire curve.
• Select option causing direct response in output to cost pressures tied to price level.

Why A is correct:

• A rise in raw material prices increases variable production costs, prompting firms to supply less at the current price level, causing a movement up and left along the AS curve (per sticky-wage AS model where input costs respond to price changes).

Why the others are wrong:

• B: Wage price rise is a fixed cost factor, shifting AS curve leftward.
• C: Productivity rise reduces unit costs, shifting AS curve rightward.
• D: Sales tax rise acts as a government policy change, shifting AS curve leftward.

Final answer: A