Level order traversal of a rooted tree can be done by starting from the root and performing breadth first search (BFS).

Explanation:
Breadth First Search (BFS):
Breadth First Search is a graph traversal algorithm that explores all the vertices of a graph in breadth-first order, i.e., it visits all the vertices at the same level before moving to the next level. It uses a queue data structure to keep track of the vertices to be visited.

Level Order Traversal:
Level order traversal is a method of visiting the nodes of a tree level by level, from left to right. In this traversal, we visit all the nodes at the same level before moving to the next level.

Procedure:
To perform level order traversal of a rooted tree, we start from the root node and enqueue it in a queue. Then, while the queue is not empty, we dequeue a node, visit it, and enqueue its children (if any) in the queue. This process continues until all the nodes have been visited.

Explanation of options:
a) Preorder traversal: Preorder traversal is a depth-first traversal method that visits the root node, then the left subtree, and finally the right subtree. It does not guarantee the nodes to be visited in level order.
b) Inorder traversal: Inorder traversal is a depth-first traversal method that visits the left subtree, then the root node, and finally the right subtree. It does not guarantee the nodes to be visited in level order.
c) Depth First Search (DFS): DFS is a graph traversal algorithm that explores all the vertices of a graph in depth-first order, i.e., it visits all the vertices along a path from the starting vertex before backtracking. It does not guarantee the nodes to be visited in level order.
d) Breadth First Search (BFS): As mentioned earlier, BFS explores all the vertices of a graph in breadth-first order, visiting all the vertices at the same level before moving to the next level. It guarantees the nodes to be visited in level order.

Therefore, option 'D' (Breadth First Search) is the correct answer for performing level order traversal of a rooted tree.