A single 802.11g access point has been configured and installed in the center of a square office. A few wireless users are experiencing slow performance and drops while most users are operating at peak efficiency. What are three likely causes of this problem (Choose three.)（）。

A. mismatched TKIP encryption
B. null SSID
C. cordless phones
D. mismatched SSID
E. metal file cabinets
F. antenna type or directio