Read the passage carefully and answer the following question:

Demographic Transition Theory is used to describe and predict the future population of any area using fertility (Crude Birth Rate) and mortality (Crude Death Rate) data in a three-staged model.

Stage I is called high fluctuating wherein both fertility and mortality are high. People reproduce more children to compensate for deaths due to epidemics and food shortages. The growth is low and fluctuating. The people are engaged in agriculture having low technology. The life expectancy is also low.

Stage II is expanding stage where fertility remains high in the beginning while mortality starts to decline due to medical and sanitation revolution. This decline in mortality causes natural increased in population. In the second half of this stage fertility also starts to decline.

In the last stage, low fluctuating growth rate is due to low fertility and low mortality. The population is stable or grows slowly. The population becomes urbanised and literate and has high technological know-how.

Identify the cause responsible for natural increase in population in the first part of the second stage of Demographic Transition.

Decline in mortality while fertility is still high

Stage II is expanding stage where fertility remains high in the beginning while mortality starts to decline due to medical and sanitation revolution. This decline in mortality causes natural increased in population. In the second half of this stage fertility also starts to decline.

During the early part of the second stage, mortality starts to decline due to medical advancements and improvements in sanitation, leading to a decrease in death rates. However, fertility remains high initially, leading to a natural increase in population as births exceed deaths.