The correct answer is: D. Social milestones vary due to culture
Different societies but they have substantial differences in their educational systems, which respond both to the dynamics of progress that were happening in different form or times in each of the societies, to the criteria culturally accepted by their citizens, the laws in force, and so on. Social milestones aren't universal.
That is why in the country of origin of Francis you enter the educational system at age 5 and in Fortune Country do it from age 8. This has nothing to do with the biology of children, nor does it necessarily depend on the psycho-social maturity of children, but both societies have different conceptions as to the way of educating the child.
