Which function does PHP perform?
A. popping the top label one hop before the egress LSR
B. popping the top label at the egress LSR
C. popping the bottom label one hop before the egress LSR
D. popping the bottom label at the egress LSR
E. popping the two topmost labels one hop before the egress LSR
F. popping the two bottommost labels one hop before the egress LSR
