All but one of the factors listed is a major contributor to world population increases. that factor is a) increased birth rate b) decreased death rate c) increase immigration to foreign countries d) an increase in the quality of medical care

D) Increase the quality of medical care.

The major cause of population explosion or increases is due to increased birth rate and decreased death rate. Due to rapid development of science and technology, the medicinal field has improved its quality in all aspects.

During past periods, birth rate was decreased due to premature delivery, fetus born death, death during pregnancy, etc. But now due to increase in the quality of medical care, these entire problems have been rectified and the birth rate has increased which has paved way for population increase.

the answer would be 3