How did one child challenge the whole world

China's one-child policy had been successful in lowering its birth rate, which has declined since the 1990s to an average of 1.5, which means on average women give birth to 1.5 children.

China's “one-child policy” (OCP) is the largest among the world's family planning programs. ... According to the World Bank, the fertility rate in China dropped from 2.81 in 1979 to 1.51 in 2000. The reduced fertility rate is likely to have affected the Chinese labor market profoundly.

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i believe the answer is d.