Final answer:
The statement that is true regarding mental disorders is that abnormal and normal behavior exist on a continuum. This reflects the complex and evolving understanding of what constitutes mental disorders, as outlined in the DSM.
Step-by-step explanation:
The correct statement regarding mental disorders is D. Abnormal and normal behavior exist on a continuum. This acknowledgement is central to the diagnostic process. Mental disorders encompass a vast spectrum of issues ranging from schizophrenia and major depression to anxiety disorders and phobias. The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM) provides criteria for these diagnoses but acknowledges that the science evolves, and so do the classifications of symptoms.
Importantly, criteria for diagnosing mental disorders are complex, and there is no single criterion that holds across all forms of abnormal behavior. The concept of normality is fluid, and behaviors can be viewed as more or less typical in different contexts or cultures. Mental health professionals, including licensed psychologists and counselors, can also conduct diagnoses, not solely psychiatrists.