Final answer:
If Nikita exhibits multiple personalities, the condition is likely dissociative identity disorder (DID), a mental illness characterized by the presence of multiple identity states that control behavior.
Step-by-step explanation:
If Nikita takes on multiple personalities, she may have dissociative identity disorder (DID). Formerly known as multiple personality disorder, DID is characterized by the presence of two or more distinct identity or personality states that continually have power over the individual's behavior. It is a severe form of dissociation and a mental process which produces a lack of connection in a person's thoughts, memory, and sense of identity.
While DID is a complex and controversial condition, it is recognized as a mental illness under the Diagnostic and Statistical Manual of Mental Disorders (DSM), which is published by the American Psychiatric Association. This manual is used by clinicians and psychiatrists to diagnose psychiatric illnesses.
In the case of Nikita, possessing multiple personalities is not indicative of obsessive-compulsive disorder, borderline personality disorder, or major depression, which have different criteria and symptoms. Therefore, the correct answer is c. dissociative identity disorder.