Quiz: Kosaraju's First DFS

In Kosaraju's algorithm, the first DFS records finish order. Why can't you just run a single DFS on the original graph and group nodes by their connected components?

1. A.Because DFS does not work on directed graphs
2. B.Because the original graph might have self-loops
3. C.Because directed reachability is not symmetric. Reaching $v$ from $u$ does not mean $v$ can reach $u$
4. D.Because a single DFS always visits all nodes