A system administrator is attempting to add a default router using the command:

route add default 192.20.20.1 0

You get the error message "Network is unreachable." The IP address of the host you are using is 192.20.20.10, and the router 192.20.20.1 is reachable using a "direct" route. The router 192.20.20.1 is on the network in question and is a viable default router.

What causes the error message "Network is unreachable"?

A.
The metric of 0 should be 1.

B.
You already have several default routers.

C.
Your default router should be reachable indirectly.

D.
You should act as the default router to your own network.

E.
Default routers can only be added through a file at boot-up .