Which four statements about the Carrier Supporting Carrier （CSC） feature are true？ （）
- AMPLS is required between the PE and CE routers that connect the backbone carrier to the customer carrier.
- BThe backbone carrier must enable the PE router to check that the packets it receives from the CErouter contain only the labels that the PE router advertised to the CE router.
- CEvery packet that crosses the backbone carrier must be encapsulated so that the packet includes MPLS labels
- DAII PE routers that link the backbone carrier to the customer carrier must run Route Target Rewrite.
- EArouting protocol is required between the PE and CE routers that connect the backbone carrierto thecustomer carrier. The routing protocol enables the customer carrier to exchange IGP routing information with the backbone carrier.