This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Social science, Mental health & Genetics, Subject name: Social & Preventive Medicine
IQ for sever mental retardation - 
Select and explain. 
A. <20, B. 20-35, C. 35-50, D. 50-70
B: 20-35
Answer: B: 20-35 
Explanation: WHO classification of Mental retardation(MR) mild MR...IQ 50-70 moderate MR ...35-49 severe MR..IQ 20-34 profound MR...IQ under 20 ref; (page no;582) 23rd edition of PARK&;s textbook of Preventive and Social medicine