**Two Tier 2 Service Providers are using a Tier 1 Service Provider for transport. MPLS is required between the Tier 2 Service Providers for label switching. In this CSC solution, which label stack is correct?
A. original IP packet, MPLS CSC transport label, MPLS VPN label, and MPLS Tier 2 transport label
B. original IP packet, MPLS Tier 2 transport label, MPLS VPN label, and MPLS CSC transport label
C. original IP packet, MPLS VPN label, MPLS Tier 2 transport label, and MPLS CSC transport label
D. original IP packet, MPLS Tier 2 transport label, MPLS CSC transport label, and MPLS VPN label
E. original IP packet, MPLS VPN label, MPLS CSC transport label, and MPLS Tier 2 transport label
