The correct answer is 1921 - 1951.The decades 1921-1951It is referred to as the period of steady population growth. Hence, Option 3 is correct.An overall improvement in health and sanitation throughout the country brought down the mortality rate.At the same time, better transport and communication systems improved distribution systems.The crude birth rate remained high in this period leading to a higher growth rate than in the previous phase.This was impressive in the backdrop of the Great Economic Depression, the 1920s, and World War II.Additional InformationThe period from 1901-1921It is referred to as a period of the stagnant or stationary phase of growth of Indias population, since in this period growth rate was very low, even recording a negative growth rate during 1911-1921.Both the birth rate and death rate were high keeping the rate of increase low.Poor health and medical services, illiteracy of people at large, and an inefficient distribution system of food and other basic necessities were largely responsible for high birth and death rates in this period.The decades 1951-1981 It is referred to as the period of population explosion in India, which was caused by a rapid fall in the mortality rate but a high fertility rate of the population in the country.The average annual growth rate was as high as 2.2 percent.It is in this period, after the Independence, that developmental activity was introduced through a centralized planning process and the economy started showing up ensuring the improvement of the living conditions of people at large.Consequently, there was a high natural increase and a higher growth rate.From the post-1981 till presentThe growth rate of the countrys population though remained high, has started slowing down gradually.A downward trend in crude birth rate is held responsible for such population growth.This was, in turn, affected by an increase in the mean age at marriage, improved quality of life particularly education of females in the country.