Is used if the concatenation of two lists is to be performed on O 1 time?

The correct answer is [c] Circular doubly linked list

Best explanation: We can easily concatenate two lists in O [1] time using singly or doubly linked list, provided that we have a pointer to the last node at least one of the lists. But in case of circular doubly linked lists, we will break the link in both the lists and hook them together. Thus circular doubly linked list concatenates two lists in O [1] time.