In a circular doubly linked list without a sentinel, which statement is true?

• A. A circular doubly linked list cannot be traversed from head to tail.
• B. The head’s prev pointer points to NULL and the tail’s next pointer points to NULL.
• C. The head’s prev pointer points to the tail, and the tail’s next pointer points to the head.
• D. There is no concept of a head in a circular doubly linked list.

Answer: (D)

In a circular doubly linked list, every node has both next and prev, and the links form a continuous loop with no NULL terminators. If you designate a starting node as the head, the node that comes just before it in the circle is the tail. Because of the circular arrangement, the head’s previous pointer points to that tail, and the tail’s next pointer points back to the head. This wraparound is what keeps the list connected in a circle and allows traversal to continue from the tail back to the head without hitting NULL. The absence of a sentinel doesn’t remove the head concept; you still have a starting point, and the pointers reflect the circular linkage rather than ending at NULL.