State which of the following topologies are not solvable: (i) 5 nodes, 10 branches, 5 independent voltage sources; (ii) 7 nodes, 12 branches, 7 indepen- dent current sources; (iii) 4 nodes, 7 branches, 4 independent current sources; (iv) 6 nodes, 9 branches, 1 independent voltage source, 3 independent current sources; (v) 5 nodes, 9 branches, 3 independent voltage sources, 2 independent. current sources.