The principal factor depressing life expectancy in developing countries has always been th
Mortality, of course, is not a perfect measure of nutritional change. Improved nutrition is only one of a number of forces that have been pushing down death rates in developing countries. Others include the upgrading of hygiene and sanitation; the extension of public health services; medical innovations; improvements in education, communications, transportation, and, in some areas, civil order. Even so, the extent to which improvements innutrition—both direct and indirect—have reduced mortality in developing countries has frequently been underestimated. For example, Sri Lanka experienced an abrupt jump in life expectancy shortly after the Second World War. Whereas this was long described as a "technical fix"—a triumph of DDT over the anopheles mosquito—years later researchers realized that abrupt and rapid drops in mortality had also taken place in Sri Lanka' s highlands, or "dry zones", where malaria had never been a serious problem. In both highlands and lowland regions health improved in tandem with access to food.
According to the author, life expectancy in developing countries is not high mainly because developing countries______.
A.have a low standard of living
B.have no public health services
C.have no public and private hygiene and sanitation
D.have low survival rates for infants and children