Which of the Following Statements About the BFD Echo Function

Which of the following statements about the BFD echo function are true? (Choose three.)

A) The local system sends a series of BFD Echo packets, and the remote system loops the packets back through its forwarding channel.
B) If the local system receives several consecutive Echo packets, it advertises a session Down event.
C) The echo function can work together with the asynchronous or demand detection mode.
D) The echo function can take the place of fault detection by sending BFD control packets.