According to Jean Piaget's theory of cognitive development, in which stage do children begin to develop an understanding of themselves as separate and distinct from the environment, alongside initial concepts of causality, time, and space?

According to Jean Piaget, the ability to use symbols for symbols (such as letting the letter 'X' stand for an unknown numeral) develops during the ______ and enables children to learn ______.

According to Jean Piaget, at which stage does a child develop hypothetical-deductive reasoning and scientific thinking begins to emerge?