Townsend, Peter, author
Pinguin Book, 1975
Buku Teks
Cunningham, Jo, author
Learning Matters, 2008
Buku Teks
Horton, Paul B., author
Appleton-Century-Crofts, 1955
Buku Teks
edited by Paul B. Horton and Gerald R. Leslie
Prentice-Hall, 1975
Buku Teks
Westhues, Kenneth, author
McGraw-Hill, 1972
Buku Teks