السلام عليكم ورحمة الله وبركاته,
Host 192.0.2.156 does not belong to any network in the routing table. So the router will forward the traffic through the default gateway. According to "show ip route" output, the default gateway is 192.168.4.1 (Gateway of last resort is 192.168.4.1 to network 0.0.0.0). Looking at the routing table (192.168.4.0/24 is directly connected, Serial2), this means that the default gateway is Serial2, so all traffic going to 192.0.2.156 will be routed through Serial2. The Answer is C. Hope that helps.