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Egocentric thinking, in the ( pre-operational, concrete operational, sensorimotor, formal operational ) stage, was illustrated by the ( three mountains task, conservation task, A-not-B task, beaker problem ). ( Four, Three, Two, One ) year old children couldn't think about other peoples perspectives. ( Hughes, DeVos, Piaget, Dasen ), however, showed that young children could cope with the task if it was more ( realistic, simple, logical, scientific ).