Identify two key factors that have contributed to the increase in average life expectancy in many developing countries over the last few decades.

Select two options: A. Wider implementation of national immunization and vaccination campaigns | B. Greater access to improved sanitation and safe drinking water sources | C. An increase in the prevalence of undernourishment in rural populations | D. A reduction in the number of skilled healthcare workers in rural clinics | E. A shift towards higher import tariffs on essential pharmaceutical drugs