Gerking, Shelby D.
Burgess, 1970
Buku Teks
Patterson, C.O. Pat
Burgess Publishing , 1973
Buku Teks
by Margaret J. Hartman [and others]
Kendall/Hunt, 1976
Buku Teks
by Willis H. Johnson...[et al.]
Holt, Rinehart and Winston, 1974
Buku Teks
McCourt, Richard M.
McGraw-Hill, 1990
Buku Referensi