Final answer:
The elasticity of demand measures the responsiveness of quantity demanded to changes in price, with the correct answer being (c) price.
Step-by-step explanation:
The elasticity of demand is defined as the percentage change in quantity demanded divided by the percentage change in price. This ratio measures how much the quantity demanded of a good or service is affected by a change in its price. So, the correct answer is (c) price, which means that elasticity of demand is the response of quantity demanded to changes in price, and not the quantity supplied, the slope of the demand curve, or the slope of the supply curve.