Which of the following should be used to ensure a device is inaccessible to a network-connected resource?

Host isolation is the most direct and effective method to ensure a device is inaccessible to a network-connected resource. It involves physically or logically separating the device from the network, preventing any communication. Disablement of unused services reduces the attack surface but doesn't guarantee complete inaccessibility if other services remain active or vulnerabilities exist. A web application firewall (WAF) protects web applications specifically and wouldn't isolate an entire device from network resources. A network-based Intrusion Detection System (IDS) monitors traffic for malicious activity and alerts administrators, but it does not prevent network access; it's a detection mechanism, not an isolation tool.