Rintoul, M. C., author
Routledge, 1993
Buku Referensi
Sharp, Mick
London Blandford 1997,
Buku Referensi
Kau, James B., author
McGraw-Hill, 1985
Buku Teks
Shilling, James D., author
South-Western, 2002
Buku Teks
Cohen, Leon W., author
D. Van Nostrand, 1963
Buku Teks