Option A configures uRPF loose mode to forward the packet. This mode allows the router to check if there is a route in the routing table that matches the source IP address of the incoming packet, regardless of the interface that is used to reach the source. This mode is suitable for networks that have asymmetric routing, where the incoming and outgoing interfaces for a packet may differ2.

Option B permits the 172.16.3.251 in the inbound ACL on interface gi0/3. This option does not resolve the issue, because it only allows the packet to pass the ACL check, but not the uRPF check. The packet will still be dropped by uRPF if there is no route to reach the source IP address via the same interface3.

Option C permits the 172.16.3.251 in the inbound ACL on interface gi0/3 to allow 172.16.3.251. This option is redundant and incorrect, because it repeats the same IP address twice in the ACL statement. It also does not resolve the issue for the same reason as Option B3.

Option D configures uRPF strict mode to forward the packet. This option does not resolve the issue, because it is the same mode that was already configured on the interface. Strict mode requires that the router has a route to reach the source IP address via the same interface where the packet was received. If this condition is not met, the packet will be dropped4.