What Is the "4-2-1" Conundrum, and Why Do Demographers Fear

What is the "4-2-1" conundrum, and why do demographers fear it?

A) Compared with the top, there are four times as many people on the bottom of the age pyramid and two times as many in the middle. Demographers fear that that the population will explode.
B) In China there are four grandparents and two parents but only one child to support them all when they retire.
C) In China in 1982, 1% of the population was over 65. In 1996 it was 2%, and now 4% of the population is over 65. The result is that there are more older people to support.
D) In China, 4% of the population works, 2% are underage, and 1% are retired. Demographers fear this will reverse.
E) Worldwide, one in four females gets an education and one in two males gets an education. Demographers fear that women will have no other option then to have children.