A.Before MPLS is enabled, the ip cef command is only requited on routers 1 and 4
B.After MPLS is enabled, the ip cef command is only required on routers 1 and 4
C.Before MPLS is enabled, the ip cef command is only required on the Ethernet 0 interfaces ofrouters 1 and 4
D.After MPLS is enabled, the ip cef command is only required on the Ethernet 0 interfaces ofrouters 1 and 4
E.Before MPLS is enabled, the ip cef command must be applied to all provider routers