The correct answer is 'Mean time to remediate' because it measures the average time taken to resolve an incident from the moment it is detected until it is fully remediated. 'Mean time to detect' refers to the time taken to detect an incident, and 'Alert volume' refers to the number of alerts received in a given time period, neither of which describe the resolution time frame. 'Critical vulnerabilities and zero-days' is not a time-based metric but rather a classification of vulnerabilities.