R & R Newkirk/Longman, 1985
Buku Referensi
Morton, Gene A.
Fishergate, 1986
Buku Teks
Black, Kenneth, author
Prentice-Hall, 2000
Buku Teks
Huebner, S. S., author
Appleton-Century Crafts, 1958
Buku Teks
Black, Kenneth, author
Prentice-Hall, 1994
Buku Teks