Spratto, George R.
Delmar Cengage learning, 2010
Buku Referensi
Wilson, Billie Ann
Prentice-Hall, 2003
Buku Referensi
edited by Jeyanth Asheervath and Dorothy R. Blevins
Appleton-Century-Crofts, 1986.
Buku Referensi
Lopez, Frank.
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Buku Teks SO
Spratto, George R.
Delmar Cengage Learning, 2012
Buku Referensi