Performing comprehensive risk assessments (B) throughout the life of a third-party contract is the most critical activity because risk posture changes over time due to evolving threats, business changes, or control degradation. CISM emphasizes that third-party risk is not static and must be continuously assessed to ensure ongoing alignment with risk appetite. Disaster recovery testing (A) and SLA updates (C) are important but limited in scope. Financial reviews (D) focus on cost rather than security risk. Periodic risk assessments enable timely identification of new risks and ensure appropriate mitigation or escalation. References: ISACA CISM Review Manual (Governance-third-party risk lifecycle management); CISM Exam Content Outline (Domain 2).