Answer
We can make a spanning tree simply by removing one of the six edges. Note that removing any one of the six edges will result in a tree.
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 has 6 vertices and 6 edges. Therefore this graph is not a tree.
However, by removing any one of the 6 edges, the graph will have 6 vertices and 5 edges. Also, the graph will still be connected and there will be no circuit. Therefore, the graph will be a tree.
For example, to make a spanning tree, we could remove the edge AB.
