Answer:
A. biological.
Explanation:
Psychology can be studied from many different perspectives. The biological perspective of studying psychology gave importance to genetics and the physical nature of human beings and animals. It is the study of human behavior that examines the nervous system, hormonal system or immune system. It is also called bio-psychology and it was the first perspective to use human genetics as the bases to study human behavior. Charles Darwin used this approach to study the role of genetics and its relation to human behavior.
As per the question, the study of testosterone and estrogen which are hormones signifies it as a study from a biological perspective.