Answer:
B.O(n).
Step-by-step explanation:
In an ADT graph the method addEdge uses an Array of list.So in the worst case and the worst will be when the list already has n elements in it.
So to add an edge we have to iterate over the list upto nth element and then add the edge after that.So it has to travel over n elements.
So we can say that the answer is O(n).