Which Statement Best Describes the Basic Premise of Behavioural Genetics

Which statement best describes the basic premise of behavioural genetics?

A) 'Your personality is all in your genes.'
B) 'Your personality is all in your environment.'
C) 'People are either very open to new experiences or avoid new experiences at all costs.'
D) 'Openness to new experience is not an either/or proposition, but represents a wide range of reactions.'