What Lead to the Development of Family Systems Therapy

What lead to the development of family systems therapy?

A) the recognition that most psychological disorders can be attributed to and cause dysfunctional relationships
B) the established importance of the interaction of nature and nurture in the development if all forms of psychopathology
C) the realization that the family environment played a role in whether or not relapse occurred
D) the observation that signs of mental illness often were seen in more than one family member