Myopia Has Become More Common Since the Advent of Public

Myopia has become more common since the advent of public schooling. Research on this phenomenon

A) has not been performed because it is unethical to try to make a child develop myopia.
B) suggests that it is the quality of indoor lighting that increases the likelihood of developing myopia.
C) suggests that extended periods of close focus, from reading books in school, causes myopia.
D) has determined that not enough outdoor time is the reason for this increase in myopia rates.