The correct answer is d. pattern of behaviour that causes people significant distress. People usually confuse abnormal behavior with unusual behavior, but behaving in a way which out of the ordinary does not necessarily mean that a person suffers from a mental or psychological disorder. Abnormal behavior is often indicative of mental and psychological disorders. According to the The Encyclopedia of Clinical Psychology, a psychological disorder is defined as an "ongoing dysfunctional pattern of thought, emotion, and behavior that causes significant distress, and is considered deviant in that person's culture or society".
