Which Piece of Evidence,if It Existed,would Rule Out Environmental Influences

Multiple Choice

Which piece of evidence,if it existed,would rule out environmental influences on intelligence

A)  Fraternal twins have different IQs from one another. 
B)  Adopted children have very different IQs from their adoptive parents. 
C)  Identical twins always have identical IQs. 
D)  Children with different diets also have different IQs.