What Was Demonstrated by a Study That Investigating Self-Efficacy in People

What was demonstrated by a study that investigating self-efficacy in people dealing with multiple sclerosis?

A) Self-efficacy is promising but has not demonstrated enough usefulness for physical illness.
B) Self-efficacy interventions can be useful for people with certain disorders.
C) The effect of self-efficacy greatly depends on the severity of a chronic condition.
D) The utility of self-efficacy is hard to gauge because it is inconsistent in people with chronic illness.