Which of the following is an example of a domain?

The choice of google.com as an example of a domain is correct because a domain refers to a distinct address on the internet that identifies a particular entity or resource. In this case, google.com is the specific address where one can access Google's website.

Domains are part of the Domain Name System (DNS) which is a hierarchical system that translates user-friendly domain names into numerical IP addresses that computers use to identify each other on the network. A domain typically consists of a second-level domain (like "google") and a top-level domain (like ".com"), coming together to form a complete web address.

The other options are not domains in the same sense. Windows is an operating system, Firefox is a web browser, and ransomware refers to a type of malicious software—all of which do not represent internet addresses but rather categories of software or threats. Therefore, google.com stands out clearly as the only valid example of a true domain within the context of this question.