Research by Seymour Kety Et Al

Research by Seymour Kety et al. (1978) indicates which of the following?

A) People who are adopted are more likely to be diagnosed with schizophrenia.
B) Environmental factors play the most important role in schizophrenia.
C) Heredity may play a role in the development of schizophrenia.
D) Symptoms of schizophrenia are more severe for people who were adopted.