Figure 2.14: Figure 2.14 (a) A graph to help illustrate the concept of a spanning tree. (b) The wiggly edges are a tree, but not a spanning tree, because vertices D and E are not part of the tree. (c) The wiggly edges are not a tree because they are not connected. All of the vertices of the graph are, however, endpoints of wiggly edges. (d) The wiggly edges are not a tree, because they contain the edges of the circuit BDCAB. All the vertices of the graph are, however, endpoints of wiggly edges. (e) The wiggly edges form a tree and include all of the vertices of the graph as endpoints of wiggly edges. Thus, the wiggly edges are a spanning tree.