Davidson, Bill, author
Harper & Row, 1961
Buku Teks
Kennedy, Richard
Macmillan Publishing Co. Inc, 1982
Buku Teks
Freedman, Lawrence, author
Oxford University Press, 2000
Buku Teks
Kennedy, Gavin
Duckworth, 1989
Buku Teks
Kennedy, Raymond
Yale University Press, 1945
Buku Referensi