Host 1 receives a file from remote server 1. Which MAC address appears as the source address in the header of the frames received by Host 1（）。
- AThe MAC address of the NIC in Host 1
- BThe MAC address of the NIC in server 1
- CThe MAC address of the Fa0/0 interface of router R1
- DThe MAC address of the s0/0/0 interface of the router R2