If the Correlation Between Identical Twins on Trait R Is

If the correlation between identical twins on Trait R is higher than the correlation between fraternal twins on Trait R, behavior geneticists conclude that:

A) genetic factors are important in the development of Trait R.
B) genetic factors are irrelevant to the development of Trait R.
C) environmental factors are irrelevant in the
development of Trait R.
D) genetic factors and environmental factors play equivalent roles in the development of Trait R.