Answer: A. Due to sanitation and agricultural advances, yet poverty and lack of family planning.
Population growth in the developing world can be associated with a lot of different factors. On the one hand, sanitation has led to less infant deaths, which means that even if births remain the same, more babies survive childhood and become adults. It is also associated with agricultural advances, which has increased the amount of food available and given the countries the opportunity to support a larger population.
On the other hand, poverty and lack of education and family planning means that many couples have more children than they desire, either because of lack of information or in order for children to help support the family.
