Perfectly elastic demand is horizontal

Steps:

• Recall that perfectly elastic demand means infinite responsiveness to price changes, shown as a horizontal curve.
• Examine each demand curve in the diagram for slope and shape.
• Identify the curve parallel to the quantity axis with no price variation.
• Select the matching option.

Why D is correct:

• Curve D is horizontal, indicating consumers buy infinite quantities at the market price but none above it, per the definition of perfectly elastic demand (elasticity coefficient = ∞).

Why the others are wrong:

• A: Downward-sloping, showing elastic but not perfectly elastic demand.
• B: Steep downward slope, indicating inelastic demand.
• C: Moderate downward slope, reflecting unit elastic demand.

Final answer: D