Refer to the exhibit. Which command must be applied to Router1 to bring the GRE tunnel to an up/up state?
A. Router1(config-if)#tunnel source Loopback0
B. Router1(config-if)#tunnel mode gre multipoint
C. Router1(config-if)#tunnel source GigabitEthernet0/1
D. Router1(config)#interface tunnel0
Correct Answer: A