Which command will ensure that External_B will be the primary router for traffic using the gateway
address of 172.16.15.20?

A.
On External_B add the command standby 1 priority 80.

B.
On External_A add the command standby 1 priority 110.

C.
On External_A add the command standby 1 priority 80.

D.
On External_B remove the command standby 1 preempt

Explanation:
The default HSRP router priority is 100, and the router with the highest priority will become active.
Lowering the priority of External_A to 80 would ensure that External_B would become the active
router with its default value of 100.