Frances lives in a country where formal schooling begins at five years of age. She travels to a foreign country where schooling only begins at eight years of age. What explains the difference in age of entrance into formal schooling between the two countries Frances has experienced?
A.Biological milestones are universal.
B.Social milestones are universal.
C.Biological milestones vary due to culture.
D.Social milestones vary due to culture.