One Evening While Walking Home from the Bus Stop, You

One evening while walking home from the bus stop, you saw a person behaving unusually. He appeared to be having a conversation with no one, and then he began cowering in terror although there seemed nothing around to be scared of. When you walked by him, he asked you if you were aware that aliens were coming that night to take over the government. Since you just took an abnormal psychology class, you suspect that this person may be experiencing the symptoms of:

A) schizophrenia.
B) dissociative identity disorder.
C) obsessive-compulsive disorder.
D) a dissociative fugue.