What would you do next to fingerprint the OS?

While attempting to discover the remote operating system on the target computer, you receive the following results from an nmap scan:

Starting nmap V. 3.10ALPHA9 ( www.insecure.org/nmap/ )
Interesting ports on 172.121.12.222:

(The 1592 ports scanned but not shown below are in state: filtered) PortStateService
21/tcpopenftp
25/tcpopensmtp
53/tcpcloseddomain
80/tcpopenhttp
443/tcpopenhttp

Remote operating system guess: Too many signatures match to reliably guess the OS.

Nmap run completed — 1 IP address (1 host up) scanned in 277.483 seconds

What would you do next to fingerprint the OS?

A.
Perform a tcp traceroute to the system using port 53

B.
Run an nmap scan with the -vv option

C.
Perform a Firewalk with that system as the target IP

D.
Connect to the active services and review the banner information

Explanation:
Most people don’t care about changing the banners presented by applications listening to open ports and therefore you should get fairly accurate information when grabbing banners from open ports with, for example, a telnet application.