The best indicator of the risk appetite and tolerance level for the risk associated with business interruption caused by IT system failures is the recovery time objective (RTO). The RTO is the maximum acceptable time or duration that a business process or an IT system can be disrupted or interrupted before it causes unacceptable impact or harm to the business. The RTO reflects the risk appetite and tolerance level for thebusiness interruption risk, as it indicates how much disruption or interruption the business can tolerate or accept, and how quickly the business needs to resume or recover the business process or the IT system. The RTO also helps to determine the priorities and requirements for the business continuity and recovery planning, and to select and implement the appropriate continuity and recovery strategies and solutions. Mean time to recover(MTTR), IT system criticality classification, and incident management service level agreement (SLA) are not the best indicators of the risk appetite and tolerance level for the business interruption risk, as they are either the measures or the outcomes of the business continuity and recovery performance, and they do not directly indicate how much disruption or interruption the business can tolerate or accept. References = CRISC Review Manual, 6th Edition, ISACA, 2015, page 50