Which of the following behaviours characterize the 'concrete operational stage' as proposed by Jean Piaget?

Conservation and class inclusion are hallmark abilities of the concrete operational stage (ages 7-11) in Piaget's theory. Children at this stage understand that quantity remains the same despite changes in appearance (conservation) and can organize objects into hierarchical categories (class inclusion). Hypothetico-deductive reasoning belongs to the formal operational stage, deferred imitation and object permanence are sensorimotor stage achievements, and make-believe play with irreversibility of thought characterizes the preoperational stage.