Upgrading end-of-support operating systemsisone of the most effective ways to reduce the attack surface. Unsupported OS versionsno longer receive security patches, making them prime targets for attackers. Removing outdated softwareensures that known vulnerabilities cannot be exploited. A (honeynet)is used for threat analysis, not reducing the attack surface. B (Group Policy)helps enforce security policies butdoes not address outdated vulnerabilities. C (High availability)focuses on uptime, not security risk reduction. Reference:CompTIA Security+ SY0-701 Official Study Guide, Security Architecture domain.