#### Answer

This graph is not a tree because this graph has a circuit.

#### Work Step by Step

A tree is a graph that is connected and has no circuits. A graph is connected when there is a path between every pair of vertices.
Let's consider the path B,C,D,B. This path starts and ends at the same vertex, so it is a circuit. This graph has a circuit.
Since this graph has a circuit, this graph is not a tree.