A. Increases and Decreases in Demand
Explanation
Panel (a) collects the changes that increase demand, shifting the whole curve out to D₁: a taste shift toward the good, a larger buying population, higher income for a normal good, a rise in the price of substitutes, a fall in the price of complements, and expectations of future scarcity or higher prices.
Panel (b) collects the mirror-image changes that decrease demand, shifting the curve in to D₁. In both panels the price of the good itself is held constant. A change in that price would move the economy along a single curve rather than shifting it.
Curve Shape
Key
D₀ (original) and D₁ (after the shift)
\(\text{Shift} \neq \text{Movement along curve}\)