You Want to Determine the Web Server and Host Operating

Multiple Choice

You want to determine the web server and host operating system of a target. For legal reasons, you worry about getting caught. A passive recon technique that cannot be detected might be a good idea.
Which of the following choices holds the least risk of detection?

A) Use the netcraft website to look up the target's host
B) Use telnet to perform a banner grab
C) Use a common scanner in "paranoid mode"
D) Call them and ask