Final answer:
The correct answer is option a. cognitive.
Step-by-step explanation:
Kumar is interested in observing changes in the intelligence levels of teenagers in his neighborhood, particularly their verbal and reasoning skills as they progress through their teenage years. In this context, Kumar is focused on the cognitive processes involved in developmental psychology.
Cognitive development in adolescence is marked by the transition to more complex thinking abilities and the capacity for abstract thought. Teenagers develop the ability to consider multiple points of view, engage in hypothetical reasoning, and question authority or societal norms.
The cognitive theory of development, proposed by Jean Piaget, suggests that our cognitive abilities develop through specific stages, culminating in formal operational thought during adolescence. Developmental psychologists study such cognitive changes, along with physical and psychosocial development, forming a comprehensive picture of human growth from conception through death.