Beard, R. M. (2006). An outline of Piaget's development psychology. Routledge.
Lua i Stíl Chicago (17ú heag.)Beard, Ruth M. An Outline of Piaget's Development Psychology. London: Routledge, 2006.
Lua MLA (9ú heag.)Beard, Ruth M. An Outline of Piaget's Development Psychology. Routledge, 2006.
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