The spouse of a patient with schizophrenia says, I don't understand how nurturing or toilet ...

The spouse of a patient with schizophrenia says, I don't understand how nurturing or toilet training in childhood has anything to do with this incredibly disabling illness.
 
  Which response by the nurse will best help the spouse understand this disorder?
  a. This illness is the result of genetic factors.
  b. Psychological stress is at the root of most mental disorders.
  c. It must be frustrating for you that your spouse is sick so much of the time.
  d. New findings show that this condition more likely has biological rather than psychological origins.