单选题What is the term "ordered control" mean regarding how MPLS LSPs are established?（）A establish starting at the egress router going back to the ingress routerB establish starting at the ingress router going downstream to the egress routerC establish when

establish starting at the egress router going back to the ingress router

establish starting at the ingress router going downstream to the egress router

establish when a router learns of a new prefix

establish when the path correctly matches the reverse path forwarding check