Brown's longitudinal work was confirmed in a cross-sectional study of 21 children. Jill and Peter de Villiers (1973) found that children who correctly use the morphemes that Adam, Eve, and Sarah had acquired late were also able to use the ones that Adam, , Eve, and Sarah had acquired earlier. The children mastered the morphemes at difference ages, just at Adam, Eve, and Sarah had done , but the order of their acquisition was very similar.