With reference to the Age-Sex Pyramid, consider the following statements:

a. A triangular-shaped pyramid with a wide base indicates larger populations in lower age groups due to high birth rates and is typical in less developed countries.

b. A bell-shaped and tapered pyramid indicates constant birth and death rates leading to a near-constant population.

c. A narrow base and a tapered top pyramid indicate low birth and death rates which can be found in developed countries.

Which of the statements given above is/are correct?