Which configuration should be done in order to improve the performance of the Cisco Unified Wireless IP Phone 7921G in a WLAN infrastructure?（）

A.nominally 30 percent to best align with Cisco Unified Communications System recommendations
B.100 percent to ensure that the VoWLAN calls can use all the available bandwidth, if needed
C.system default of 75 percent
D.40 to 60 percent
E.voice CAC should be left disabled unless wired QoS is configured

A.configure WLAN setting to enable WMM
B.configure WLAN Aironet information elements enabled
C.configure global 802.11b/g or 802.11a，or both，voice CAC
D.configure WLAN QoS Platinum
E.configure DTIM = 2