Over time, the hierarchy of firms has tended to move from

Billie's Billiard Barn has seen its business slow down ever since Patti's Ping Pong Parlour opened up across the street

Since the opening of Patti's Ping Pong Parlour, the opportunity cost of shooting pool at Billie's Billiard Barn has ________ for Billie's customers who also like to play ping pong. A) not changed. B) decreased. C) fallen to zero. D) increased.

If muffins and bagels are substitutes, a higher price for bagels would result in a(n)

a. increase in the demand for bagels. b. decrease in the demand for bagels. c. increase in the demand for muffins. d. decrease in the demand for muffins.