Demand Curve Holds All Else Constant Except Price

Steps:

• Recall that a demand curve graphs quantity demanded versus price of the good, assuming ceteris paribus.
• Identify ceteris paribus factors: income, tastes, prices of related goods remain fixed.
• Note that movement along the curve occurs due to price changes of the good itself.
• Eliminate options A, B, C as they are held constant; select D as the variable.

Why D is correct:

• By definition, the demand curve shows how quantity demanded responds to changes in the good's own price (law of demand).

Why the others are wrong:

• A: Consumers' incomes are held constant to isolate price effects.
• B: Tastes and preferences are assumed fixed under ceteris paribus.
• C: Prices of substitutes remain unchanged to focus on the good's price.

Final answer: D