Using FTP passive mode， after the client opens thecommand channel （port 21） to the FTP server and requests passive mode， what will be the next step？ （）

• A、 The FTP server sends back an acknowledgment （ACK） to the client
• B、 The FTP server allocates a port touse for the data channel and transmit that port number to the client
• C、 The FTP server opens the data channel to the client using the port number indicated by the client
• D、 The FTP client opens the data channel to the FTP server on Port 20
• E、 The FTP client opens the datachannel to the FTP server on Port 21