Children Who Have Disorder X and Were Adopted at Birth

Children who have disorder X and were adopted at birth are studied to determine the degree of genetic contribution to disorder X. Which of the following results is most likely to support the hypothesis of genetic influence in the etiology of disorder X?

A) The rate of the disorder in these adopted children is the same as in the general population.
B) The rate of the disorder is greater in the biological siblings of these children than in adoptive siblings.
C) The rate of the disorder is greater in the adoptive siblings of these children than in their biological siblings.
D) The rate of the disorder is the same in the biological and adoptive siblings of these children.