Soule, Charles E.
Irwin, 1994
Buku Teks
Bucher, Charles A
Times Mirror/Mosby College, 1985
Buku Teks
Vilbrandt, Frank C.
McGraw-Hill Kogakusha, Ltd., 1959
Buku Teks
Grimes, Charles E.
Australian National University, 1987
Buku Teks
Kluwer Academic Publishers, 1990
Buku Teks