Concept:A movement along the same demand curve can only be caused by a change in the price of the commodity itself.
Explanation:Points x and z lie on the same demand curve for milk.
The movement from x to z is therefore a change in quantity demanded, not a shift of the curve.
This movement occurs only because of a change in the price of milk.
When the price of milk decreases, the quantity demanded increases, causing a movement along the curve from x to z.
Changes in taste, income, or weather conditions would shift the whole demand curve instead.
Answer:B. a decrease in price of milk.
