Atkinson, Toby D., author
Springfield, 1994
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Merriam-Webster's, Incorporated, 1993
Buku Referensi
Munter, Mary, author
Prentice-Hall, 1982
Buku Referensi
Ewald, Helen Rothschild, author
Prentice-Hall International, 1997
Buku Teks
Locker, Kitty O., author
McGraw-Hill, 2013
Buku Teks