What Was Demonstrated in Rosenhan's Study Using "Pseudopatients

What was demonstrated in Rosenhan's study using "pseudopatients"?

A) Our mental health system is biased toward seeing mental illness in all potential patients.
B) Most mental patients are extensively observed before an initial diagnosis is made.
C) It is extremely difficult to successfully fake the symptoms of serious mental illness.
D) Mental hospital staff often spend a great deal of time interacting with patients.