Assume The queue abstract data type $($ADT$)$ supports the following operations:

enqueue$($e$)$: Insert element e at the rear of the queue.

dequeue$()$: Remove element at the front of the queue but do not return at the output; an error occurs

if the queue is empty.

front$()$: Return, but do not remove, a reference to the front element in the queue; an error occurs if

the queue is empty.

size$()$: Return the number of elements in the queue.

empty$()$: Return true if the queue is empty and false otherwise.