Refer to the exhibit.
The Bigtime router is unable to authenticate to the Littletime router.
What is the cause of the problem?
A . The usernames are incorrectly configured on the two routers.
B . The passwords do not match on the two routers.
C . CHAP authentication cannot be used on a serial interface.
D . The routers cannot be connected from interface S0/0 to interface S0/0.
E . With CHAP authentication, one router must authenticate to another router. The routers cannot be configured to authenticate to each other.