GATE 2024 DA Q.14: official answer

Consider performing depth-first search (DFS) on an undirected and unweighted graph $G$ starting at vertex $s$. For any vertex $u$ in $G$, $d[u]$ is the length of the shortest path from $s$ to $u$. Let $(u,v)$ be an edge in $G$ such that $d[u]<d[v]$. If the edge $(u,v)$ is explored first in the direction from $u$ to $v$ during the above DFS, then $(u,v)$ becomes a ______ edge.