In the market for tacos,a normal good,you observe that the equilibrium price and quantity have increased.This can be caused only by:

A) an increase in the price of beef.
B) an increase in the wages of taco shop workers.
C) fewer taco shops.
D) an increase in the incomes of people who eat tacos.

Since tacos are a normal good, an increase in the incomes of people who eat tacos would lead to an increase in demand, causing an increase in both the equilibrium price and quantity. A, B, and C would not directly affect demand for tacos and therefore would not cause an increase in equilibrium price and quantity.