When planning for voice deployments with the Cisco Unified Wireless IP Phone 7921G handset in amultifloor building with a WLAN that operates at an 11 MB/s data rate， how many decibelsreferenced to 1 milliwatt of same-channel separation are recommended between floors？（）

A.13 dBm
B.19 dBm
C.25 dBm
D.31 dBm