Which of the Following Is the BEST Definition of an Incident

Which of the following is the BEST definition of an Incident?

A) Loss of ability to operate to specification, or to deliver the required output
B) A change of state which has significance for the management of a Configuration Item or IT Service
C) A warning that a threshold has been reached, something has changed, or a failure has occurred
D) An unplanned interruption to an IT service or reduction in the quality of an IT service