In hierarchical routing with 4800 routers, what region and cluster sizes should be chosen to minimize the size of the routing table for a three layer hierarchy? (A) 10 clusters, 24 regions and 20 routers (B) 12 clusters, 20 regions and 20 routers (C) 16 clusters, 12 regions and 25 routers (D) 15 clusters, 16 regions and 20 routers