#### Answer

To make a spanning tree from the original graph, we can use the edges AD, BE, CF, DE, and EF. The spanning tree has 6 vertices and 5 edges and every edge is a bridge. The spanning tree is connected and there are no circuits.

#### Work Step by Step

One characteristic of a tree is the following: If the graph has $n$ vertices, then the graph has $n-1$ edges. The original graph in this exercise has 6 vertices so the spanning tree must include all 6 vertices and we need to include 5 edges in the spanning tree.
To make a spanning tree from the original graph, we can use the edges AD, BE, CF, DE, and EF. The spanning tree has 6 vertices and 5 edges and every edge is a bridge. The spanning tree is connected and there are no circuits. Therefore, this is a valid spanning tree.
This is one spanning tree, but other spanning trees are possible.