What must be configured to enable DHCP requests to an external DHCP server?

A controller is provisioned as a Layer 3 device for wireless clients. Wireless clients are not able to receive an IP address when they connect to the WLAN.

What must be configured to enable DHCP requests to an external DHCP server?
A . IP helper on the controller management VLAN
B . IP helper address on the user VLAN interface
C . IP helper address on the controller uplink interface
D . IP helper address on the upstream switch

Answer: D