An organization is using a centralized DHCP server for all IP phones. However, when the IP
phones are powered up, the phones are unable to obtain an IP address. Which CLI command
should be in the router configuration to ensure that the IP phones are able to reach the DHCP
server?

A.
router(config)#helper-address

B.
router(config-if)#ip helper-address

C.
router(config-if)#helper-address

D.
router(config)#ip helper-address