Refer to the graphic.
Host A is communicating with the server. What will be the source MAC address of the frames received by Host A from the server?
Host A and the Server are on different subnets and are separated by routers, so the MAC address of the Server will never get back to Host A: the router will decapsulate the frames that the Server sends. The router will re-encapsulate the packets from the Server and and put its own MAC address on the outbound interface (e0) in the frames. Host A will see the MAC address of router interface e0.