A machine’s ONLY external interface is configured with an address of 192.168.5.1 and a netmask of 255.255.255.0.  No slots are available for expansion. Which of the following procedures should be performed to make it function as a gateway？（）

A.Enable ipforwarding only
B.Configure an alias on the same interface and enable ipforwarding
C.Add a second interface into the same subnet and enable ipforwarding
D.Add a second interface into a different subnet， and enable ipforwarding