Piaget's Original Interest the Subject of Children's Intelligence Was Aroused

Piaget's original interest the subject of children's intelligence was aroused by:

A) his observation of the differences in intellectual "style" between his two equally intelligent daughters.
B) his personal experience as a precocious child.
C) his fascination with the question as to why children often gave incorrect answers to intelligence test items.
D) his desire to understand his own, relatively mediocre academic record as a child.