Answer:
a. Harlan, who is testing a theory about the development of prejudice
Explanation:
Basic research refers to a form of research that carried out in order to prove or disprove a theory that already proposed in the past. This type of research is most commonly used in finding out patterns among common occurrence that people often overlooked.
(in option A, harlan conducted the research to prove whether the theory about the development of prejudice is correct)
In order to achieve the conclusion, Harlan need to set up a control group filled with independent variables that can influence the development of prejudice.