Final answer:
The demographic group that had the most dramatic reduction in deaths during the 20th century is infants and young children, due to major public health improvements, including vaccines, better sanitation, and advancements in medical care. The correct answer is option a.
Step-by-step explanation:
During the 20th century, significant advancements were made in the field of public health, leading to noticeable changes in mortality rates across different demographic groups. Through improvements in sanitation, medical innovations such as vaccines and antibiotics, and better access to healthcare, especially for infants and young children, the demographic group that witnessed the most dramatic reduction in deaths is a) Infants and young children.
The demographic transition resulted from many factors, including decreases in infant mortality rates. As economic security increased and the well-being of people improved, fewer children were born because fewer needed to survive to take care of their parents in old age. Furthermore, the empowerment and education of women played a crucial role in reducing birthrates. These changes led to an overall decrease in family size from an average of six children in the early 19th century to 1.6 in the 20th century in developed countries. Consequently, the death rates among infants and young children drastically declined.