Two Clinicians Are Asked to Diagnose a Patient Who Shows

Two clinicians are asked to diagnose a patient who shows symptoms of obsessive-compulsive disorder (OCD) and depression. The first clinician believes that depression is an important cause of OCD and so does not diagnose the patient with OCD. The second clinician believes that depression is a by-product of OCD but not a root cause. Therefore, she diagnoses the patient as having OCD. This example illustrates that

A) our beliefs and background knowledge influence how we categorize things.
B) clinicians are often mistaken in their diagnoses.
C) theories are often fallible and so should not be depended on in many situations.
D) theories are not involved when placing a test case into a particular category.