What is required for a Cisco IP Phone to obtain an address from a Cisco CallManager running the DHCP service if they are not both on the same subnet?

A.
Default router

B.
Option 150 with the IP address of the CallManager

C.
Option 86 with the IP address of the TFTP server

D.
IP helper address

Explanation:
IP helper address modifies the IP phone DHCP broadcast to a unicast so the request can be routed to other subnets where DHCP server sits on.