The correct answer is A. Networks get extended using VPNs. In legacy architectures, security controls such as firewalls and appliance stacks are typically anchored to the enterprise network perimeter. When users need to work from outside that protected network, the common historical solution is to extend the network to them through a virtual private network (VPN) . This gives the remote user a path back into the corporate environment so the existing perimeter controls can still be used. Zscaler’s Universal ZTNA architecture explicitly contrasts Zero Trust with this legacy model by stating that Zero Trust allows users to access applications without sharing network context or routing domain with them.

That contrast is important because VPNs preserve a network-centric trust model. Instead of granting access only to a specific application, VPNs often place users onto a routable enterprise network. Zero Trust replaces this with application-specific, identity- and context-based access. A reliable Wi-Fi connection alone is not a security architecture, single sign-on does not create the network path, and saying remote work is impossible is incorrect because VPNs were the legacy answer. Therefore, the best answer is that legacy networks are extended using VPNs .