Answer:
Population growth rates fall with development because countries become better educated and have better resources
Step-by-step explanation:
As a country develops, it's population has better access to a quality education, and it's women typically become more empowered. These two factors lead to women joining the workforce and not having kids as early in life, or having less kids. They also typically get better medicine and more open access to birth control.
Both of these factors allow women to plan their families, as opposed to being seen as child-producing machines. This is why the average child per family in the United States (a developed country) is 1.8, while in Zimbabwe (developing), it's about 3.7.