Which age group contributes directly to population growth through the process of reproduction?

Consider the following statements regarding the age structure of a population: (a) A large pre-reproductive group indicates future population growth. (b) Equal pre-reproductive and reproductive groups indicate demographic stability. (c) A large post-reproductive group suggests rapid population expansion. (d) Age structure is graphically represented by age pyramids. Which of the statements given above are correct?

A population pyramid with a narrow base and a relatively wider middle or top section typically indicates which of the following?