Supply Elasticity Measures Responsiveness Steps:

• Calculate PES values: X (+1) is unit elastic; Y (-0.2) is inelastic with negative sign, indicating low responsiveness and inverse reaction.
• For a price fall, quantity supplied typically decreases; elasticity shows how much output adjusts.
• Compare magnitudes: |PES_X| = 1 > |PES_Y| = 0.2, so X's supply adjusts more readily.
• Lower |PES| for Y means output changes less, making adjustments harder.

Why C is correct:

• Definition: Elasticity of supply gauges ease of output adjustment; Y's lower |PES| (-0.2) means smaller response to price fall, so increasing output is harder than for X (+1).

Why the others are wrong:

• A: Substitutes affect demand elasticity, not supply.
• B: 20% price rise causes X output to rise 20% (PES +1), Y to fall 4% (-0.2); no "greater decrease" for both.
• D: Concerns demand response and buyers, not supply elasticity.

Final answer: C