Traversal of a graph is different from tree becausea)BFS of a graph uses queue, but a time efficient BFS of a tree is recursiveb)DFS of a graph uses stack, but inorder traversal of a tree is recursivec)All of the mentionedd)There can be a loop in graph so we must maintain a visited flag for every vertex

The traversal of a graph is different from a tree due to the following reasons:

a) Breadth-First Search (BFS) of a graph uses a queue data structure. This is because BFS explores all the vertices of a graph at the current level (i.e., breadth) before moving on to the vertices at the next level. However, a time-efficient BFS of a tree is recursive, which means it uses a call stack (not to be confused with a stack data structure).

b) Depth-First Search (DFS) of a graph uses a stack data structure. This is because DFS explores a path as far as possible (i.e., depth) before backtracking. But, an inorder traversal of a tree is recursive, which means it uses a call stack.

c) All of the mentioned points are correct.

d) There can be a loop in a graph, so we must maintain a visited flag for every vertex to avoid getting stuck in an infinite loop. This is not necessary in a tree because trees are acyclic by definition, which means they do not contain any loops.