Where is the MPLS label imposed?()
A.after the Layer 3 header and before the Layer 2 payload
B.after the Layer 3 header and before the Layer 4 payload
C.after the Layer 2 header and before the Layer 1 payload
D.after the Layer 1 header and before the Layer 2 payload
E.after the Layer 2 header and before the Layer 3 payload