Answer: d)MTTD
Explanation: MTTD(Mean Time To Detect) is the time for the discovery of the problem in a system. It is basically the average time until the problem is noticed by someone. For e.g.- if there is a problem in a computer system at 9:00 am and the problem is noticed at 9:10 am by then user then the MTTD is 10 minutes . So, MTTD gives the mean time for which the system remains available for use.
