In 802.11n, what does fat channel intolerance indicate?

A.
Clients hearing this information must transmit in the secondary channel only.

B.
Both the clients and access points hearing this information must no longer aggregate
MPDU frames.

C.
Access points hearing this information must use the default 40 MHz channel bandwidth.

D.
Access points hearing this information must prohibit the use of 40 MHz channels.

Explanation:
Reference: http://forums.anandtech.com/showthread.php?t=249626 (last post on the page)
Fat Channel Intolerant Communicates to surrounding networks that this WiFi adapter is not
tolerant of 40MHz channels in the 2.4GHz band.