This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Bias is unlikely to invalidate cohort studies used to assess risk of exposure because - 
Select and explain. 
A. Data collection is prospective, B. Large number of subjects is usually included, C. Exposure is usually determined prior to disease occurrence, D. Actual relative risk can be determined
C: Exposure is usually determined prior to disease occurrence
Answer: C: Exposure is usually determined prior to disease occurrence 
Explanation: None