Answer:
c) cognitive
Step-by-step explanation:
Cognitive development: The term cognitive development refers to the process through which a child explore, think, and figure out different things in life.
When a child is being cognitively developed then it means that the child has developed problem-solving techniques, skills, dispositions, knowledge, memory, reasoning, intelligence, and language development that helps a child in understanding the world around them.
Cognitive development also includes the brain development of a child.
In the question above, the researcher is interested in the cognitive development of the subject(s).