अपने संज्ञानात्मक विकास के सिद्धांत में, जीन पियाजे संज्ञानात्मक संरचनाओं को ______ के रूप में समझाते हैं।

According to Jean Piaget's theory of Cognitive development, at which stage can most children 'operate on operations' and develop hypothetico-deductive thinking?

A child understands that adding four to five yields nine, but cannot yet perform the reverse operation of taking four from nine. According to Jean Piaget, this limitation indicates which stage of cognitive development?