Determinants of Individual Demand

Steps:

• Define demand as the quantity of a product a consumer is willing and able to buy at various prices, holding other factors constant.
• Identify key non-price determinants: consumer's income (affects purchasing power) and willingness to buy (reflects preferences or tastes).
• Distinguish demand (entire relationship) from quantity demanded (movement along the curve due to price changes).
• Evaluate choices: A includes both income and willingness, fully capturing demand shifters.

Why A is correct:

• Per the law of demand, the demand curve is derived from a consumer's income and willingness (preferences), which determine the schedule of quantities at different prices.

Why the others are wrong:

• B: Price affects quantity demanded along the curve, not the demand curve itself.
• C: Includes income but omits willingness, ignoring preferences as a core determinant.
• D: Solely price, which only traces movements on the demand curve, not its position.

Final answer: A