基礎ECON-DEMA-015
The price of bubble tea rises and, at the same time, consumer incomes fall. Bubble tea is a normal good. What must be true?
A. Quantity demanded falls for two reinforcing reasons, but the demand curve itself shifts only because income fell.✓ 答案
B. The demand curve becomes upward sloping.
C. Both changes are movements along the original demand curve.
D. The income change shifts supply, and the price change shifts demand.
解說
A higher price of bubble tea is a movement along the demand curve: quantity demanded falls. Lower income, for a normal good, shifts the whole demand curve left. Only the non-price change shifts demand. The two effects both reduce quantity, but they are not the same kind of change.