Which one of the following options is the best way to ensure this setting is saved across system restarts?

On a Linux router, packet forwarding for IPv4 has been enabled. After a reboot, the machine no longer forwards IP packets from other hosts. The command:

echo 1 > /proc/sys/net/ipv4/ip_forward

temporarily resolves this issue.

Which one of the following options is the best way to ensure this setting is saved across system restarts?
A . Add echo 1 > /proc/sys/net/ipv4/ip_forward to the root user login script
B . Add echo 1 > /proc/sys/net/ipv4/ip_forward to any user login script
C . In /etc/sysct1.conf change net.ipv4.ip_forward to 1
D . In /etc/rc.local add net.ipv4.ip_forward = 1
E . In /etc/sysconfig/iptables-config add ipv4.ip_forward = 1

Answer: C