The Higher Fertility Rates in Low-Income Countries Illustrate the Fact

The higher fertility rates in low-income countries illustrate the fact that low-income countries:

A) have more crowded urban centers than high-income countries.
B) have more agricultural than industrial economies, making children important sources of labor.
C) are more industrialized than middle-income countries, so they need more wage earners.
D) are more likely to send children to school for longer periods of time.