The Board , 1982
Buku Teks
Lee, Sangheon, author
Blackwell Publishing, 2017
Artikel Jurnal
Moore, Wilbert E. (Wilbert Ellis), author
Prentice-Hall, 1967
Buku Teks
edited by Emrys Jones
Oxford University Press, 1975
Buku Teks
edited by Paul B. Horton and Gerald R. Leslie
Prentice-Hall, 1975
Buku Teks