You are configuring controller redundancy and are about to adjust the fast heartbeat timer. What does an AP do when the configured heartbeat timer interval expires? Select the best response.

A.
Sends data channel controller packets, if it does not get a response it does a fast failover to the secondary controller.

B.
Sends an MPING to both its secondary and primary controller, then it does a fast join to whichever responds first.

C.
Checks to see if it has received any control packets from the controller; if not, it then sends a fast echo request to its configured secondary controller.

D.
Checks to see if it has received any data packets from the controller; if not, it sends a fast echo request to its configured primary controller.