问题：

[单选] 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.