Demand Curve Shift Due to Income Change

Steps:

• Recognize the shift from D1 to D2 indicates a change in demand, not a movement along the curve.
• Recall that demand shifts rightward from non-price determinants like income, tastes, or prices of related goods.
• Evaluate options: A and B affect supply; C affects quantity demanded via price.
• Identify D as the factor increasing demand for vegetables, a normal good.

Why D is correct:

• An increase in real incomes raises purchasing power, shifting the demand curve right for normal goods per the income effect in demand determinants.

Why the others are wrong:

• A: Changes supply curve, not demand.
• B: Poor harvest decreases supply, shifting supply curve left.
• C: Price change causes movement along the existing demand curve.

Final answer: D