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.