Concept:A rightward shift in the demand curve indicates a rise in demand at every price level, caused by a non-price factor.
Explanation:When a buyer's income increases, their purchasing power improves.
For a normal good, a higher income leads to greater quantity demanded at each possible price.
Therefore, the entire demand curve shifts to the right.
This is a change in demand, not merely a change in quantity demanded.
A decrease in the price of the good itself causes a downward movement along the same demand curve, not a shift.
Changes in population size or availability of substitutes affect demand but are not the most direct cause given here; an income rise is the clearest trigger for a rightward shift.
Answer:B. an increase in the income of the buyer