Bromhead, Peter
Longman, 1992
Buku Teks
Leonard, Dick
Macmillan, 1992
Buku Teks
edited by Lawrence Butler and Harriet Jones
Heinemann , 1994
Buku Referensi
edited by Lawrence Butler and Harriet Jones
Heinemann ,
Buku Referensi
Schlesinger, Arthur Meier, author
Alfred A. Knopf, 1958
Buku Teks