Which of these is not a DFS$-$based algorithms for identifying strongly connected components?

a$)$ Perform a DFS traversal of the digraph given and number its vertices in the order they become dead ends.

b$)$ Reverse the directions of all the edges of the digraph.

c$)$ Perform a DFS traversal of the new digraph by starting $($and$,$ if necessary, restarting$)$ the traversal at the highest numbered vertex among still unvisited vertices.

d$)$ Implementing the two topological sorting algorithms in the language of your choice. Run an experiment to compare their running times.