A feasible solution is reached in transportation problem when O a. all demand and supply constraints are satisfied. O b. the number of filled cells is one less than the number of rows plus columns. O c. all of the improvement indices are greater than or equal to zero. d. all the squares are used. O e. the solution yields the lowest possible cost. The minimal spanning tree problem determines the: a. maximum amount that can be transported along any one path. O b. minimum amount that should be transported along any one path. O c. minimum total branch lengths connecting all nodes in the network. Od shortest distance between a source node and a destination node