Routers R1 and R2 are on the same network segment, and both routers use interface GigabitEthernet0/0. If R1 loses communication to R2, which two items should you check as you begin troubleshooting?

A.	Verify that R2 is using 802.1q encapsulation.
B.	Verify that the GigabitEthernet0/0 interfaces on R1 and R2 are configured with the same subnet mask.
C.	Verify that the R1 GigabitEthernet0/0 interface is up and the line protocol is down.
D.	Verify that R1 and R2 both are using HDLC encapsulation.
E.	Verify that the R1 GigabitEthernet0/0 interface is up and the line protocol is up.