Solution

The correct answer is option 4.

Explanation:

Depth First Search (DFS) is graph traversal algorithm uses stack data structure.

Option I : a b e g h f  : visit a; insert connected node of a, b;  insert connected node of b, e ;  insert connected node of e, g ;  insert connected node of g, h ; insert connected node of h, f .

Option II : a b f e h g : visit a; insert connected node of a, b; insert connected node of b, f ; Next to insert the connected node of f, which is either g or h; but e is not possible.

Option III : a b f h g e : visit a; insert connected node of a, b;  insert connected node of b, f ;  insert connected node of f, h ;  insert connected node of h, g ; insert connected node of g, e .

Option IV : a f g h b e: visit a; insert connected node of a, f;  insert connected node of f, g ;  insert connected node of g, h ;  insert connected node of h, b ; insert connected node of b, e .