The world population in $1900$ was ........ billion,which increased rapidly to ........ billion in $2000$ and reached ........ billion in $2011$.

In the world population, how many people are added per year?

$A$: Population of India crossed one billion in May $2000$.
$R$: It is the result of a rapid decline in death rate,maternal mortality rate $(MMR)$,and infant mortality rate $(IMR)$,as well as an increase in the number of people in the reproductive age.

At the time of independence,our population was approximately ........... billion,which reached near ............ billion in the year $2000$ and crossed ........... billion in $2011$.

In India,the population growth:

In India,if the marriage age is changed to $21$ years,then: