Niles, Olive S.
Georgia Scott 1984
Buku Teks
Raja Nazrin Shah
RNS Publications Sdn Bhd, 2006
Buku Referensi
Chin, Kon Yit
Jugra Publications, 2003
Buku Referensi
Niles Christensen [and others]
Illinois Scott, Foresman , 1984
Buku Teks
Schodek, Daniel L.
MIT Press, 1988
Buku Teks