Given a `Queue` data structure with `enqueue` and `dequeue` operations. What is the element returned by the last `dequeue` operation in the following sequence?  ```     Queue q;     q.enqueue('A');     q.enqueue('B');     q.dequeue();     q.enqueue('C');     q.dequeue();     q.enqueue('D');     q.enqueue('E');     q.dequeue();     ```