The population of India at the time of Christ was approximately

Which one of the following is not a consequence of population explosion?

The main cause of population explosion in the world is:

In India,the population crossed the one billion mark in May $2000$. The probable reasons for this are a decline in:
$A.$ Maternal mortality rate $(MMR)$
$B.$ Infant mortality rate $(IMR)$
$C.$ Number of people in the reproductive age group
$D.$ Death rate

$A$: 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.

Which of the following can be taken as characteristic demographic features of the developing countries?
$(a)$ High fertility rate
$(b)$ Rapidly rising mortality rate
$(c)$ Very young age distribution
$(d)$ Rapid population growth
$(e)$ Rapidly falling mortality rate
$(f)$ Very old age distribution