When McDonald's runs a special for hamburgers, reducing the price of Big Macs to $0.99 with all other factors held constant,

a) It will lead to an increase in the quantity of Big Macs demanded.
b) It will lead to a decrease in the quantity of Big Macs demanded.
c) It will not affect the demand for Big Macs.
d) It will cause an increase in the supply of Big Macs.