What component is used to connect remote users to the IPO via a WAN?

The correct choice, which is the VPN (Virtual Private Network), is essential for securely connecting remote users to the IPO (IP Office) via a WAN (Wide Area Network). A VPN creates a secure, encrypted tunnel over the internet, enabling remote users to access the IPO system as if they were within the local network. This secure connection is critical for protecting sensitive data transmitted over potentially unsecured networks, ensuring that remote communications remain private and secure.

While routers play a role in directing traffic and firewalls help secure the network perimeter, neither serves the specific function of providing secure, remote access like a VPN does. Modems facilitate the connection to the internet but do not provide the security and encryption features that a VPN offers for remote user access. Thus, a VPN is the best solution for connecting remote users to the IPO in a secure manner.