Which is the correct way to define a default route to 10.10.10.1 for a Linux host?

Which is the correct way to define a default route to 10.10.10.1 for a Linux host?

A.
ifconfig eth0 defaultgw 10.10.10.1

B.
ifconfig default_route=10.10.10.1

C.
route default add gateway=10.10.10.1

D.
route add default gw 10.10.10.1