On what device in the MPLS network does the MPLS forwarding medium voltage label ( PUSH ) operation occur ?

On what device in the MPLS network does the MPLS forwarding medium voltage label ( PUSH ) operation occur ?
A . The packet enters the MPLS network at the LER on device
B . On all LSR devices in the middle of the MPLS network
C . The packet leaves the MPLS network address LER on device
D . On all devices of the MPLS network

Answer: A

Explanation:

push-swap-pop