Which type of server must be associated with an NS record?

The correct answer highlights the requirement for a Domain Name System (DNS) server to be associated with a Name Server (NS) record. An NS record is specifically designed to delegate a zone to a particular DNS server, indicating which server is responsible for handling queries related to that domain or subdomain.

When a DNS lookup occurs, it must know which DNS server to contact for the information associated with a domain. This process is crucial for translating human-readable domain names into IP addresses, enabling users to access websites and services effectively.

In contrast, the other types of servers listed—FTP, web, and database servers—do not have a direct role in the DNS resolution process or the functionality of NS records. They handle specific tasks such as file transfer, serving web content, and managing database operations, but none of them are responsible for DNS delegation in the way that a DNS server is. Therefore, understanding the pivotal role of a DNS server linked to an NS record is key to grasping how domain name resolution functions within networking.