I think the Answer is truly B.
Backcross, the mating of a hybrid organism, offspring of genetically unlike parents,with one of its parents or with an organism genetically similar to the parent.
Behavioural genetics is the study of the effects of genes as well as well the environment on the behaviour of the individuals. The scientists who study the Behavioural genetics are known as behavioural geneticists.
In this case Dr. Hakim is studying the influence of genes and the environment on the aggression, which is a kind of behaviour. Hence, Dr. Hakim is a behavioural geneticists, and he works in in the field of behavioural genetics.
The reason both of these are valid scientific hypotheses is because A) scientists with different educational backgrounds may put forth different hypotheses to explain the same data.
This approach in science is vital in making progress and has helped to explain many phenomena in the past. When scientists explain data using different approaches, they come to a more comprehensive conclusion.
