Question

Pick the odd one out of the below choices:
Accept-Encoding
Referrer
Cache-control
Nmap

Answer 1

Accept and Referrer is odd

Answer 2

Option 4.  

Nmap is a Network Mapper which is open source scanner security used to find out services and hots on a computer of various network.

Accept-Encoding is a HTTP request header which encode the content.  

Referrer is URL data taken from HTTP header file by identifying the website links use from the web pages.

Cache-control is a header file is used to check directives form caching requests and responses.