which of the four routers shown in the graphic should a default route be configured, assuming that a routing protocol is being used to distribute the default route?

Refer to the exhibit:

Communication with the Internet is vital to all networks belonging to the corporation. On which of the four routers shown in the graphic should a default route be configured, assuming that a routing protocol is being used to distribute the default route?

A.
A

B.
B

C.
C

D.
ISP