Jean Berko's Discovery That Young Children Correctly Add Inflectional Endings

Jean Berko's discovery that young children correctly add inflectional endings to nonsense words (e.g., wugs as the plural form of wug) suggests that children

A) acquire general rules that they then apply to even unfamiliar words.
B) acquire grammar primarily through imitation and reinforcement.
C) correctly apply inflectional rules to unfamiliar words before familiar words.
D) invent grammars that seem to fit best with unfamiliar input.