Three of the four events described below might reasonably be expected to shift the demand curve for Tacos to a new position. One would not shift the demand curve. The single exception is:

a. a change in people's tastes with respect to Tacos.
b. an increase in the money income of beef consumers.
c. a widespread advertising campaign undertaken by the producers of a product competitive with Tacos.
d. a fall in the price of Tacos.

d