The correct answer is A. estimate future growth.
Forecast by analysts, retention growth model and historical growth rates are all methods used to estimate future growth. A forecast by analysts is a prediction of future growth based on the analysis of historical data and current trends. A retention growth model is a mathematical model that estimates future growth based on the assumption that a certain percentage of customers will continue to use a product or service in the future. Historical growth rates are the average annual growth rates of a company or product over a period of time.
Option B is incorrect because option A is more specific. Option C is incorrect because option A is more general. Option D is incorrect because option A is not about estimating the growth ratio, but about estimating future growth.