-Which of the Following Best Explains Why the Dependency Ratio

-Which of the following best explains why the dependency ratio in South Asia has been declining?

A) The longer life expectancy has allowed people to work for more years,thus not being dependent on others for social services.
B) The decreasing birth rate has resulted in fewer children dependent on social services.
C) The life expectancy in South Asia has been declining because of natural disasters and diseases,so there are fewer elderly citizens to take care of.
D) The increasing population in the region has resulted in more working-age people who depend on social services.