Rachel Has Been Experiencing Episodes of Paranoia and Hallucinations

Rachel has been experiencing episodes of paranoia and hallucinations. She claims that someone is entering her house and tampering with her furnace. She also says that she can smell the person's scent through the vents. Her clinician gathered information about previous history of mental illness and substance abuse. Why is it important to gather this additional information?

A) To determine a differential diagnosis
B) To assess whether Rachel requires hospitalization
C) To help the patient understand the importance of good mental health
D) To rule-out the need for a physical examination