$19$

$2$ points

While executing DFS$,$ you pop a vertex u from the Stack. We find that $u$ is not already closed and $u$ has an edge to $x.$ Currently, level $[u]=5,$ level $[x]=4,x$ is already closed, and $x$ is on the stack. After the edge is relaxed, level $[x]=$

and $x$

$2$ points

While executing DFS$,$ you pop a vertex $u$ from the Stack. We find that $u$ is not closed and $u$ has an edge to $x.$ Currently, level $[u]=5,$ level $[x]=4,$ and $x$ is on the stack. After the edge is relaxed, level$[x,$ and $x$