A research team is investigating the relationship between diet and mood, specifically focusing on how the intake of omega-3 fatty acids might influence symptoms of depression. Their preliminary findings indicate that participants with higher omega-3 levels reported lower scores on depression scales. The study also collected data on participants' daily calorie intake, their preference for organic foods, their sleep patterns, and their exercise routines.
For the research team's study focusing on how omega-3 fatty acids affect symptoms of depression, which of the following collected data is *most relevant*?
A) Participants' daily calorie intake.
B) Participants' preference for organic foods.
C) Participants' omega-3 levels and depression scale scores.
D) Participants' sleep patterns.
E) Participants' exercise routines.