As our population ages and the birth rates slow down, we will experience: a rapid population growth.

Sorry, but your question is not really clear but if you are asking for the meaning of "Rapid Population Growth", then here it is:

Rapid population growth has serious economic consequences. It encourages inequities in income distribution; it limits rate of growth of gross national product by holding down level of savings and capital investments; it exerts pressure on agricultural production and land; and it creates unemployment problems.

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