Mercury is a hypothetical store that sells athletic shoes, particularly shoes for runners. Mercury is distinctive in the training of its sales staff. The store has a variety of diagnostic tools, including weight distribution analysis and slow-motion replay, and the staff are trained to use those tools to help customers figure out exactly which shoe will be best for them. Mercury also carries a wide assortment of shoes from the full range of athletic shoemakers, some of which are otherwise-hard-to find models. Although Mercury is an independent store, it is part of a buying cooperative that enables it to obtain its shoes from suppliers at volume discount prices that would otherwise be available only to large chains. Mercury sponsors a variety of races in its greater metropolitan area, the largest of which is a high profile annual marathon. Of the following list of Mercury's activities, which two have the greatest potential for co specialization?
(a) Diagnostic skills of staff
(b) Buying cooperative membership
(c) Broad product assortment
(d) Race sponsorship