Refer to the exhibit. The Hamilton Hair Emporium was having difficulty hearing during conference calls. This configuration adjustment was made, and now the company is experiencing sound distortion. What is the cause?（）

• A、The gain functionality applies to outbound audio packets. Distortion is created when an external participant causes echo. 
• B、The distortion is unrelated to the gain functionality. Rather, it is a result of the company trying to maintain too many conference calls at one time. 
• C、This functionality cannot discriminate between a local VoIP source that requires volume gain and a CO-powered PSTN source that does not require volume gain. 
• D、This functionality cannot discriminate between a remote VoIP or Foreign Exchange Office source that requires volume gain, and a remote VoIP or IP phone that does not require volume gain.