Whitten, Kenneth W.
Saunders College, 1992
Buku Teks SO
Umland, Jean B.
Brooks/Cole, 1999
Buku Teks SO
Paul, Martin A.
Harcourt, Brace & World, 1967
Buku Teks SO
Russell, John B.
McGraw-Hill, 1981
Buku Teks SO
Umland, Jean B.
St. Paul West, 1993
Buku Teks SO