Identify a true statement about responsive supply chains.

a$.$ They use only a few, large distribution centers to generate economies of scale.

b$.$ They use optimization models that minimize costs of routing products from factory through distribution centers to retail stores and customers.

c$.$ They are designed for efficiency and low cost by minimizing inventory and maximizing efficiencies in process flow.

d$.$ They are supported by information technology that provides real$-$time information to managers across the supply chain.