Final answer:
A fall in the price of Tacos does not shift the demand curve, but instead leads to a movement along the demand curve.
Step-by-step explanation:
A change in any one of the underlying factors that determine what quantity people are willing to buy at a given price will cause a shift in demand. The exception in this scenario would be option d, a fall in the price of Tacos. A decrease in price does not shift the demand curve, but instead leads to a movement along the demand curve.