Stuart, Richard B.
Research Press Company, 1972
Buku Teks
Piaget, Jean, 1896-1980
Routledge & Kegan Paul, 1975
Buku Teks
Ritzen, Jozef
Anthem Press, 2005
Buku Teks
Bianki, V.
Foreign Languages Publishing, [date of publication not identified]
Buku Teks
Conrad, Joseph, 1857-1924
Methuen, 1956
Buku Teks