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
All of following are advantages of case control study except-a) Cheaperb) Less time consumingc) Possible to study many diseasesd) Less chances of bias 
Select and explain. 
A. bd, B. cd, C. ab, D. bd
B: cd
Answer: B: cd 
Explanation: None