$G$ is an undirected graph with vertex set $\{v1, \ v2, \ v3, \ v4, \ v5, \ v6, \ v7\}$ and edge set $\{v1v2,\ v1v3,\ v1v4\ ,v2v4,\ v2v5,\ v3v4,\ v4v5,\ v4v6,\ v5v6,\ v6v7\ \}$. A breadth first search of the graph is performed with $v1$ as the root node. Which of the following is a tree edge?
- $v2v4$
- $v1v4$
- $v4v5$
- $v3v4$