The scenario where college students reduce how much detergent they use for each load of laundry in response to higher detergent prices describes a movement along the demand curve. This is because the change in quantity demanded (using less detergent) is directly caused by a change in the price of detergent itself, with other factors held constant. Such a response is a classic example of a movement along the demand curve rather than a shift of the entire demand curve, which would require changes in other determinants like income, tastes, or prices of related goods