David Wants to Look at Genetic Influences on IQ, So

David wants to look at genetic influences on IQ, so he administers a battery of tests to Frank and Fred, who are fraternal twins; Sidney and Sheldon, who are identical twins; and Larry and Harry, who are non-twin brothers. David's supervisor asks him to make a guess about which set of siblings will most likely have the most similar IQs. David's best guess would be

A) Frank and Fred.
B) Sidney and Sheldon.
C) Larry and Harry.
D) Since they're all siblings, the correlation should be about the same for all pairs.