A web server must be accessible to untrusted outside users. What can be done to isolate this host and any additional hosts with similar requirements from more secured hosts on a network?

C. Create a DMZ, add necessary hosts.

Explanation:

According to my experience with information technology and cyber-security, I can say that in this situation you can create a DMZ and add the necessary hosts. A DMZ or Demilitarized zone is a network that is used in order to connect the necessary hosts in the network to an untrusted external network like the internet, while at the same time protecting the hosts.