" Serial 1/0 is up line protocol Down " what is the possible reason for this error ?
A. Ensure that the serial cable is correctly plugged in to the interfaces. B. Apply the clock rate 56000 configuration command to the serial0/1 interface of R1. C. Configure the serial0/1 interfaces on R1 and R2 with the no shutdown command. D. Change the address of the serial0/1 interface of R1 to 18.104.22.168. E. Change the subnet masks of both interfaces to 255.255.255.240