Let T be a rooted tree with 13 nodes, in which each node has either two or zero children. The leaves of this tree are 1,2,3,4,5,6,7, and the non- leaves are A, B, C, D, E, F; the names of these leaves and non-leaves are not in any particular order. We run the algorithm explore(u), where u is the root of T. This algorithm generates recursive calls to explore(u), in the following order A, E, B, 2, 7, F, 1,5, D,4,C,6,3. What is the number of nodes in the subtree rooted at node F? (Note that the node F is included in the count.) Select one: O a. 5 O b.3 O c. 1 O d. 7