Dr. Simon's team was conducting a study on the relationship between iron and vit

Dr. Simon's team was conducting a study on the relationship between iron and vitamin C intakes and the rate of infections in a small population of college students. They needed to assess the intake of these two nutrients in the subjects. What would be a good method to employ?
A. Have the participants pick out their favorite foods from a list.
B. Take the participants out to lunch and observe what each one orders.
C. Give the participants a food frequency questionnaire to fill out.
D. Interview family members closely associated with the subjects and ask for their opinions on what the subjects typically ate.