Which reason for this issue is true?

You are setting up a Cisco access point in repeater mode with a non-Cisco access point as the parent and you use this interface configuration on your Cisco access point. You are getting the following error message.

Which reason for this issue is true?

%DOT11-4-CANT_ASSOC: Interface Dot11Radio0, cannot associate: No Aironet Extension IE
A . “dot11 extension aironet” is missing under the interface Dot11Radio 0 interface
B . When repeater mode is used, unicast-flooding must be enabled to allow Aironet IE communications.
C . The parent AP MAC address has not been defined.
D . Repeater mode only works between Cisco access points.

Answer: A

Explanation:

from: http://www.cisco.com/c/en/us/td/docs/wireless/access_point/12-2_11_JA/configuration/guide/b12211sc/ s11rep.html