Hay, Julie
Open University Press, 2007
Buku Teks
Haimann, Theo
South-Western Pub., 1982
Buku Teks
Boyd, Branford B.
McGraw-Hill , 1984
Buku Teks
Leonard , Edwin C., Jr.
South-Western Cengage Learning, 2013
Buku Teks
Terry, George Robert
Richard D. Irwin, 1982
Buku Teks