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
Evidence based medicine, which of the following is not useful -a)  Personal exposureb)  RCTc)  Case reportd)  Meta-analysise) Systemic review 
Select and explain. 
A. a, B. ac, C. ad, D. b
B: ac
Answer: B: ac 
Explanation: None