Final answer:
Delusional disorder is characterized by non-bizarre delusions, such as feeling persecuted or spied on, without the other symptoms distinctive of schizophrenia or bipolar disorder. It is treated through psychotherapy and sometimes medication.
Step-by-step explanation:
The type of disorder characterized by reasonably believable, non-bizarre delusions, such as being spied on, cheated on, or conspired against, is C) Delusional disorder.
Unlike schizophrenia, which includes symptoms like hallucinations, difficulty thinking, and problems with social situations, delusional disorder is marked specifically by the presence of delusions without the other hallmark symptoms of schizophrenia.
Treating delusional disorder typically involves psychotherapy and may include medications, though the course can vary based on individual circumstances.
Considering other options, Bipolar disorder is associated with dramatic shifts in mood and energy, and Obsessive-compulsive disorder (OCD) involves repetitive thoughts and behaviors. Neither is primarily characterized by non-bizarre delusions. Therefore, Delusional disorder is the correct answer.