Before Walmart's Entry into the Retail Pharmacy Business Which Drove

Before Walmart's entry into the retail pharmacy business which drove down prices,existing pharmacies

A) were operating efficiently,so this is an example of predatory pricing.
B) were colluding on price,so this is an example of a contestable market.
C) were not operating as efficiently as afterwards,so this is not a case of predatory pricing.
D) did not advertise but were forced to do so by the new competition.