How does 802.11r or fast BSS transition reduce the amount of time required for a client to roam?

A.
by allowing a client to pre-associate to multiple APs, which eliminates the need for the client to
associate to a new AP when roaming

B.
by giving a new client priority in the AP scheduling mechanism, which gives a new client a
faster response from the new AP

C.
by reducing the amount of authentication messaging between a client and a new AP, which
means that the client does not need to renegotiate keys with the new AP

D.
by adding hand-off communications between the APs, which means that the old AP notifies the
new AP when the client is about to roam