In the network as shown in the figure below, the data traffic is forwarded as STA-HAP-HAC-upper network before roaming, and the forwarding method is direct forwarding, and the home agent is configured on the AC. After three-layer roaming, what is the direction of data forwarding traffic?
A . STA-FAP-FAC-Upper Network
B. STA-FAP-FAC-HAC-FAC-Upper Network
C. STA-FAP-FAC-HAC-Upper Network
D. STA-FAP-FAC-HAC-HAP-HAC-upper network