What Is "The Most Astonishing, Agreed-Upon, and Dramatic Finding of Developmental

What is "the most astonishing, agreed-upon, and dramatic finding of developmental psychology"?

A) Growing up in the same family makes very little difference - at least in personality traits.
B) Siblings more likely to share the same general personality characteristics than two children selected at random.
C) Siblings, even identical twins, are completely uninfluenced by their genetic heritage.
D) Twins are as likely to share the same IQ as are their non-twin siblings.