[quote="Rubina11"]
By examining sets of identical twins in recent studies, mental disorders such as schizophrenia and autism have been found to be the results of variations in gene expression and not simply a matter of genetic inheritance.
A. By examining sets of identical twins in recent studies, mental disorders such as schizophrenia and autism have been found to be
b. By examining sets of identical twins in recent studies, mental disorders such as schizophrenia and autism were found as being
c. Mental disorders such as schizophrenia and autism were examined in sets of identical twins in recent studies and has been found to be
d. Recent studies that examined sets of identical twins have shown that mental disorders such as schizophrenia and autism are
e. Recent studies that examined sets of identical twins has shown that mental disorders such as schizophrenia and autism are
source : Gmat prep plus 2019[/quote
Option D is the correct answer. It does not contain any errors related to the subject-verb agreement.