Reliability is a measure of:
A. The availability of a service or component
B. The level of risk that could impact a service or process
C. How long a service or component can perform its function without failing
D. A measure of how quickly a service or component can be restored to normal working

C.
D is for maintainablility.
Reliability: A measure of how long a Configuration Item or IT Service can perform its agreed Function without interruption. Usually measured as MTBF or MTBSI.
Maintainability: A measure of how quickly and Effectively a Configuration Item or IT Service can be restored to normal working after a Failure. Maintainability is often measured and reported as MTRS.

C正解！D是Maintainability。 Maintainability is often measured and reported as MTRS.

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英文不好。。需要提高。。