When do populations grow exponentially

it depends on birth rate and population history of the city or country

Explanation:

In exponential growth, a population's per capita (per individual) growth rate stays the same regardless of population size, making the population grow faster and faster as it gets larger. In nature, populations may grow exponentially for some period, but they will ultimately be limited by resource availability.

i think the answer is b.

trachea, alveoli, lung capillaries, arteries