Whit Which the following is a necessity to a successful service level agreement $($SLAs$)?$

A The language and temms used in the SLA should be commonly understood by all parties

B Base the Sld on system$-$based metrics that are useful to the senvice provider

C$.$ In order to promote consistent senvice$,$ they should be carried forward, unchanged, from one

D vague largets, such as those related to user experience, should be avoided