According to the Results of Research Involving Twins and Family

According to the results of research involving twins and family members, which of the following has been suggested regarding sexual orientation?

A) Homosexual men tend to have more gay relatives on their father's side of the family than on their mother's side of the family.
B) If a child has one gay parent, the child's chance of being gay rises by approximately 70 percent, even if the child is not raised by that parent.
C) Genes may play at least some role in determining a person's sexual orientation.
D) Homosexual individuals have fewer homosexual siblings than heterosexual individuals because the siblings are able to observe the difficulties associated with being gay, and this encourages them to choose to be heterosexual.