Module $8$: Population and Community Dynamics

$13.$ The world population reached seven billion in $2011.$ At current growth rate, it is expected to reach eight billion by $2024$ and nine billion by $2037.$

However, many projections predict that the world population will level off at around $9$ billion individuals.

Why is the world population expected to level off?

A$.$ The Earth's carrying capacity is estimated at $9$ billion individuals, when the global birth rate and death rate become equivalent.

B$.$ Recent technological and medical advances led to increased life expectancy, allowing individuals to live longer.

C$.$ More than a third of the world population is expected to be aged $60$ years or above in $2100.$

D$.$ The global fertility rate has been decreasing for the past $20$ years and is expected to decline even further.