An analyst wants to identify hosts that are connecting to the external FTP servers and what, if any, passwords are being used.

Which of the following commands should the analyst use?
A. tcpdump λ∈"X dst port 21
B. ftp ftp.server λ∈"p 21
C. nmap λ∈"o ftp.server λ∈"p 21
D. telnet ftp.server 21