How could you use a web server to help in identifying the OS that is being used?

John has performed a scan of the web server with NMAP but did not gather enough information to accurately identify which operating system is running on the remote host. How could you use a web server to help in identifying the OS that is being used?

A.
Telnet to port 8080 on the web server and look at the default page code

B.
Telnet to an open port and grab the banner

C.
Connect to the web server with an FTP client

D.
Connect to the web server with a browser and look at the web page

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.