What is penultimate hop popping?

A.
A process run on the ingress router that assigns the label to the packet.

B.
A process run on the P-router that removes a label before forwarding the packet to the egress router.

C.
A process run the ingress router that sets the TTL value to 255 to hide the core routers from a traceroute.

D.
A process run on the egress router that pops (sets) the TTL value in the Layer 3 header to the value that is contained in the top label TTL value.

Explanation:

Traffic Engineering Components
A router capable of supporting MPLS is known as Label Switching Router (LSR). The LSR, found just before the last LSR in the MPLS clouds, is known as the penultimate hop. The end-to-end MPLS path is known as Label Switched Path (LSP). LSP is originated at the head-end router and terminates at the tail-end router.
Reference:
http://www.cisco.com/en/US/tech/ CK4 36/ CK4 28/technologies_white_paper09186a00800a4472.shtml