How are services protected in a legacy scenario when they are discoverable on the public...

The correct answers are A, C, and D . In a legacy architecture, applications that are exposed and discoverable on the public Internet are usually protected by building a DMZ (demilitarized zone) and placing multiple security technologies in front of the service. This commonly includes a large security stack made up of separate appliances or services for functions such as load balancing, firewalling, distributed denial-of-service (DDoS) protection, and related edge security controls. A web application firewall (WAF) is also a standard protective element in these public-facing designs because it adds inspection and protection for web-based attack patterns and internet-originated abuse.

Option B, DAST , is not a correct answer because Dynamic Application Security Testing is a testing and assessment method, not a live architectural protection control that sits inline to defend exposed services in production. Zero Trust architecture contrasts with this legacy model by removing direct public discoverability and reducing dependence on a complex exposed edge stack. Instead of defending openly exposed applications with layered perimeter tools, Zero Trust aims to make applications less discoverable and access more identity- and policy-driven.