Which statement best describes echo?（）

• A、Echo is the discernable leak-through of your own Rx path into your own Tx path. 
• B、Echo is the discernable leak-through of the packets of your Rx path into your own Tx path. 
• C、Echo is the nonaudible leak-through of the packets of your Rx path into your own Tx path. 
• D、Echo is the audible leak-through of the packets from the transmit path into your own receive path. 
• E、Echo is the nonaudible leak-through of the packets of your Tx path into your own Rx path.