http://www.oreillynet.com/network/2001/07/13/examples/net_2nd_quiz.html

Q: A socket requires an IP address, a port number and...
A: TCP/IP Protocol

This is clearly not a correct answer since sockets can be opened on UDP/IP, and even potentially on non-IP protocols (though I've never seen it done).

You may also want to make the distinction in the article that UDP ports and TCP ports have no relation to one another (i.e., port 80 in UDP doesn't have anything to do with HTTP).