Answer:
B.O(n).
Explanation:
If the graph is represented by adjacency matrix then we can find all the neighbors of a given vertex in O(n) time because each row in adjacency matrix consists the track of the neighbors.If the other vertex is a neighbor then it contains 1 in adjacency matrix if not it contains 0.So we have to iterate over that row of the vertex to find the neighbors.
The answer to your question is a shot
