Dr farah is an educational psychologist who is interested in studying the potential causal relationship between doing homework and academic achievement. in january, dr. farah has her students report their fall gpa (a measure of academic achievement) and estimate how many hours

In this context, a probable reason for Dr. Farah's choice not to conduct an experiment is because It would be unethical to manipulate whether students are told to do homework for a semester.
Even though the mainpulation is important for the data, it could has the potential of destroying the subject's life in the future.

Ithink it's a, but i might be wrong

Where are the subjestions