Over a 2 month period, Parent Limited made 25 separate share purchases of Sub Corporation in an attempt to acquire control of Sub. What is the appropriate treatment of the numerous small purchases? a. The cost method should be used until a controlling interest is acquired. b. The purchases should all be grouped together and treated as a single block purchase. c. An acquisition differential must be computed following each purchase. d. The equity method must be adopted retroactively once 20% ownership is obtained.