Which Definition of Pain Is the Foundation for the Planning

Which definition of pain is the foundation for the planning of nursing care for the client in pain?

A) Pain is whatever the experiencing person says it is, existing whenever he says it does.
B) Client's self-report is the single best indicator of pain.
C) A feeling of distress, suffering, or agony, caused by stimulation of specialized nerve endings.
D) Its purpose is chiefly protective; it acts as a warning that tissues are being damaged and induces the sufferer to remove or withdraw from the source.