In a growing population of a country, Pre-reproductive individuals are more than the reproductive individuals. Reproductive and pre-reproductive individuals are equal in number. Pre-reproductive individuals are less than the reproductive individuals. Reproductive individuals are less than the post-reproductive individuals.

When there is growing or expanding type of population, the number of pre-reproductive individuals is very large, number of age reproductive individuals is moderate, while post-reproductive individuals are fewer. Triangular type of age pyramid shows that population is growing. The rate of growth depends upon the size of pre-reproductive population. Thus, the correct answer is option B.