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: Surgery
If annual growth rate of population is 1.2%, the population is likely to get doubled in: 
Select and explain. 
A. 18--20 years, B. 20--23years, C. 28--35 years, D. 47 -- 50 years
D: 47 -- 50 years
Answer: D: 47 -- 50 years 
Explanation: Rate Annual GR % Yrs required Stationary No growth - Slow growth 0.5 >139 Moderate growth 0.5-1 139-70 Rapid growth 1-1.5 70-47 Very rapid growth 1.5-2 47-35 Explosive growth 2-2.5 35-28 Explosive growth 3-3.5 23-20 Explosive growth 3.5-4 20-18