Which statement is correct? a) a change in demand is a movement along the demand curve, and a change in quantity demanded is a shift of the demand curve. b) both a change in quantity demanded and a change in demand are movements along the demand curve, only in different directions. c) both a change in quantity demanded and a change in demand are shifts of the demand curve, only in different directions. d) a change in quantity demanded is a movement along the demand curve, and a change in demand is a shift of the demand curve.

The correct answer is option D.

Explanation:

A change in the quantity demanded is shown by a movement along the same demand curve. A change in quantity demanded happens because of a change in the price of the commodity while other factors affecting demand remain constant.

A change in the demand is shown by a shift in the demand curve. It happens when the price level remains the same but other factors change.

The other factors affecting demand for a commodity are the income of the consumer, population, tastes, and preferences, etc.