The Adult Stages of Development Proposed by Levinson and Vaillant

The adult stages of development proposed by Levinson and Vaillant may not have taken into account differences in the social clock.This means that their results:

A) may not be valid for the subjects in their studies because the subjects' social clocks were not assessed.
B) are not valid for both men and women born during the same time period as the subjects in their studies.
C) may not be valid for those born in a different historical period than the subjects in their studies.
D) are valid for any adult because the social clock has not changed significantly since the time setting of their studies.