.U.S. Govt. Print. Off, 1968
Buku Teks
Wang, Gungwu, author
Panglaykim Fundation, 1997
Buku Teks
Ranney, Austin, author
Harcourt, Brace and Company, 1956
Buku Teks
Bone, Hugh A., author
McGraw-Hill, 1965
Buku Teks
May, John D.
Duxbury Press, 1972
Buku Teks