Suppose That the Presence of a Particular Gene Is a Necessary

Suppose that the presence of a particular gene is a necessary cause for the occurrence of schizophrenia. Which of the following statements is TRUE?

A) The gene is also a sufficient cause for the occurrence of schizophrenia.
B) There are other things besides this gene that can cause schizophrenia.
C) Most people with schizophrenia will have that gene.
D) A person with that gene may or may not become schizophrenic.