Which of the following statement is correct?

Question $3$Select one:

A$.$

In most developed countries, the mismatch in timing between the mortality and fertility reductions led to a large multiplication population.

B$.$

Both fertility and mortality in the developing world have declined quickly relative to rates in the currently rich countries.

C$.$

IIn many developing countries, the fertility transition if far from complete.

D$.$

All of the above.