Routers R1 and R2, currently EIGRP neighbors over their Fa0/0 interfaces (respectively),both use EIGRP authentication. Tuesday at 8 p.m. the neighborship fails. Which of the following wo uld not be useful when investigating whether authenticationhad anything to do with the failure？（）

• A、debug eigrp packet
• B、show key chain
• C、show ip eigrp neighbor failure
• D、show clock