Which of the Following Statements Correctly Describes the Corresponding MPLS

Which of the following statements correctly describes the corresponding MPLS TTL processing mode?

A) On an MPLS VPN, if the structure of the MPLS backbone network needs to be shielded, the Uniform mode is recommended for VPN packets.
B) In Uniform mode, when IP packets enter an MPLS network, the ingress node decrements the IP TTL by one and the MPLS TTL field has a fixed value.
C) The TTL field in an MPLS label serves the same function as that in an IP packet header. That is, the TTL is used to prevent loops on an MPLS network.
D) In Pipe mode, when IP packets enter an MPLS network, the ingress node decrements the IP TTL by one and copies this new value to the MPLS TTL field.