Asocial psychologist would study why the leadership in a business is struggling the academic performance of students in high school the link between depression and lack of exercise why people in lines at the grocery store don't talk to each other

A social psychologist would study about the reason behind the people at grocery store of not communicating with each other.  

Explanation:

A social psychologist is the one who studies about the influence of actual or imaginary presence of people and environment on the other people’s thoughts and behaviors. They deal with the complex human thoughts about social interactions.

People behave differently in different human company and environment. We as humans tend to communicate more when we are around our family and friends, because we feel comfortable and secure with them.

Whereas, the people in the line at a grocery store don’t talk to each other because they don’t know each other personally. This social setting makes them uncomfortable to speak to each other.

i believe the answer would be 'd'.

hope this !