Artikel Jurnal
Macneil, Ian R.
[Publisher not identified], 1966
Buku Teks
edited by Christian P. Potholm and Richard A. Fredland
University Press of America, 1980
Buku Teks SO
Europe Publications Limited, 1992
Buku Referensi
Rogers, Margaret
Oceana Publications, 1969
Buku Teks