In an independent supply chain, the participants collaborate solely on the interactions between the immediate customer and supplier. On the other hand, in a vertical marketing system: a. firms work together with a common focus on the customer or operation of the supply chain. b. ownership may overlap, but the emphasis is on working toward common goals and objectives. c. long-term relationships are more important than gaining a temporary advantage. d. supply chain members work as a unified system. e. All of these.