Which of the following is TRUE about the ping  -f command?（）

• A、 It is useful for diagnosing data dependent problems by filling the packet with the byte pattern following the "f" in the command line. 
• B、 It is useful for flooding from slow character based terminals since it only displays a dot "." for each packet sent in fast mode. 
• C、 It is useful for flooding from slow character based terminals since it only displays a dot "."       for each packet sent and a backspace on returned in fast mode. 
• D、 The command can only be run by root.