The standard of living risen most steeply since the mid-twentieth century in the developing nations.
A developing nation is a nation that is less industrialized, holds less economic power, and may have a lower Human Development Index.
The countries which are facing the beginning of industrialization are called Developing Countries. Developed Countries have a high per capita income and GDP as compared to Developing Countries.
Thus, option B is true, as the standard of living risen most steeply since the mid-twentieth century in the developing nations.
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