जीन पियाजे द्वारा संज्ञान में परिवर्तन को प्रभावित करने वाले निम्नलिखित में से किस कारक को प्रस्तावित नहीं किया गया है?

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?