正解:D
Explanation
A service level agreement (SLA) defines response time, escalation points, and performance metrics. An SLA is a contract between a service provider and a customer that specifies the level and quality of service that will be delivered. An SLA typically includes metrics such as availability, reliability, throughput, latency, security, etc., as well as penalties or remedies for failing to meet them. An SLA also defines how issues will be reported and resolved, how often reviews will be conducted, and how changes will be communicated.