According to Piaget, When a Concrete-Operational Thinker Is Presented with the "Balance

According to Piaget, when a concrete-operational thinker is presented with the "balance beam" problem he or she

A) can appreciate the significant impact of both weight and distance from center, but cannot understand their inverse relationship.
B) can appreciate the significant impact of weight but not distance from center.
C) can appreciate the significant impact of distance from center but not weight.
D) can appreciate the significant impact of both weight and distance from center, and can understand their inverse relationship.