Henry, who is 6 years old, understands that 4+5=9; he does not, however, understand that 5+4 also equals 9. This is an illustration of which of Piaget's concepts, in which of Piaget's stages?
- object permanence in Piaget's sensorimotor stage
- Operation in Piaget's preoperational stage
- Conservation in Piaget's concrete operational stage
- Operations in Piaget's concrete operational stage