In which of the following scenarios would MAC filtering be MOST effective as a part of wireless security？ （）

A.A public place where guests are free to access the wireless network.
B.A small office where a defined number of specific wireless devices are used.
C.A meeting room where various company users will access the wireless network during meetings. 
D.An office where some users are unable to use WPA encryption due to older wireless cards so they use MAC filtering.