Which of the following options lists the steps in PPP session establishment in the correct order?（）

A. Optional authentication phase, link establishment phase, network layer protocol phase.
B. Network layer protocol phase, link establishment phase, optional authentication phase.
C. Network layer protocol phase, optional authentication phase, link establishment phase.
D. Link establishment phase, network layer protocol phase, optional authentication phase.
E. Link establishment phase, optional authentication phase, network layer protocol phase.
F. Optional authentication phase, network layer protocol phase, link establishment phase.