Answer:The statement III,described change in quantity demanded, statement IV described change in demand.
Explanation: The change in quantity demanded is otherwise known as the movement along the demand curve, it is an increase or decrease in the quantity demanded of a commodity as a result of rise or fall in price. change in the quantity demanded of a commodity is affected only by price,while all other factors affecting demand remain constant.
Change in demand is when various quantity of goods are demanded at a particular price.change in demand is affected by all other factors affecting demand except price.in other words,all other factors affecting demand will bring about an increase or decrease in the quantity of goods demanded. A change in demand will cause the demand curve to shift either to the right or to the left.