Suppose we implement a queue using a singly linked list; assume the list maintains references to the head and tail nodes. Select the operations to use to implement the queue operations most efficiently:

enqueue$/$offer:

a$)$ add node before current head node

b$)$ remove current head node

c$)$ add node after current tail node

d$)$ remove current tail

dequeue$/$poll:

a$)$ add node before current head node

b$)$ remove current head node

c$)$ add node after current tail node

d$)$ remove current tail