Refer to the exhibit.
Router>enable
Router#configure terminal
Router(config)#hostname R1
R1(config)#username R2 password cisco
R1(config)#interface serial 0/0/0
R1(config-if)#encapsulation ppp
R1(config-if)#ppp authentication chap
R1(config-if)#exit
Router>enable
Router#configure terminal
Router(config)#hostname R2
R2(config)#username R1 password cisco
R2(config)#interface serial 0/0/0
R2(config-if)#encapsulation ppp
R2(config-if)#ppp authentication pap
R2(config-if)#exit
Based on the configurations shown, why is the serial link in up/down status?