Refer to the exhibit. A Cisco Aironet Wireless LAN Client Adapter has been installed and configured  through the ADU on the PC. The Aironet System Tray Utility （ASTU） has been enabled during the  installation and the icon appears in the system tray area in the lower right of the desktop. What is the  significance of the icon？（）

• A、 It indicates that the radio of the client adapter is disabled.
• B、 It indicates that the client adapter is not associated to an access point or another client. 
• C、 It indicates that the client adapter is associated to an access point or another client， but the user is not  EAP authenticated.
• D、 It indicates that the client adapter is associated to an access point or another client， that the user is  authenticated if the client adapter is configured for EAP authentication， and that the signal strength is  excellent or good.
• E、 It indicates that the client adapter is associated to an access point or another client， that the user is  authenticated if the client adapter is configured for EAP authentication， and that the signal strength is fair.
• F、 It indicates that the client adapter is associated to an access point or another client， that the user is  authenticated if the client adapter is configured for EAP authentication， and that the signal strength is poor.