Based on Current Research, Which Statement Is Most Justified

Based on current research, which statement is most justified?

A) Genetics increase a person's vulnerability to develop schizophrenia.
B) Genetics may not be sufficient for schizophrenia, but everyone who develops schizophrenia must have some number of "schizophrenia genes."
C) Genetics cannot play a significant role in the cause of schizophrenia because most people with the disorder have no close relatives who have it.
D) Genetics play such a strong role that they are a sufficient condition for schizophrenia.