When does a "change in quantity demanded" occur?

A "change in quantity demanded" occurs specifically as a result of a change in the price of the good itself, which is the central concept behind the movement along the demand curve. When the price of a good decreases, consumers are typically willing and able to purchase more of that good; conversely, if the price increases, the quantity demanded typically decreases. This relationship is represented graphically as movement along the demand curve rather than a shift of the curve itself, which is indicative of other factors influencing demand, such as income changes or preferences. Therefore, option C accurately captures the economic principle that defines a change in quantity demanded.