Which of the following factors contributed to the study of child development in the twentieth century?

A) The beginning of public education led to a demand for knowledge about what and how to teach children of different ages.
B) Parents were having more children and researchers became interested in the effects of family size on children's well-being.
C) Pediatricians were pressured by insurance companies to improve children's health, which inspired nutritional research.
D) High rates of childhood depression inspired new areas of research into children's anxieties and behavior problems.

A