What is Cisco CKM (Centralized Key Management) used for?

A.
to allow an access point to act as a TACACS server to authenticate the client

B.
to avoid configuring PSKs (Pre-Shared Key) locally on network access devices and to
configure a PSK once on a RADIUS server

C.
to provide switch port security

D.
to allow authenticated client devices to roam from one access point to another
without any perceptible delay during re-association

Explanation:
Using Cisco Centralized Key Management (CCKM), an access point configured to provide
Wireless Domain Services (WDS) takes the place of the RADIUS server and authenticates
the client so quickly that there is no perceptible delay in voice or other time-sensitive
applications
http://www.cisco.com/c/en/us/td/docs/wireless/access_point/12-
2_13_JA/configuration/guide/s12213sc/s13roamg.html