What did china use to stop their population for rapidly growing?

But the relative size of these three Chinese population groups of 160 million will soon change. As a result of the country’s low fertility rates since the early 1990s, China has already begun experiencing what will become a sustained decline in new entrants into its labor force and in the number of young migrants. The era of uninterrupted supplies of young, cheap Chinese labor is over. The size of the country’s population aged 60 and above, on the other hand, will increase dramatically, growing by 100 million in just 15 years (from 200 million in 2015 to over 300 million by 2030). The number of families with only one child, which is also on a continued rise, only underscores the challenge of supporting the growing numbers of elderly Chinese.

The answer i think is d

Iam pretty sure it is c. 2000 bce