When Adoption Studies of Schizophrenia Contain All the Necessary Controls

When adoption studies of schizophrenia contain all the necessary controls and measurements,

A) the role of genes is found to be negligible.
B) index subjects are more likely to develop schizophrenia than the control subjects.
C) the environment is found to be a more important determinant of psychological health than family history.
D) no significant effects are seen.