Conover, Hobart H.
Allyn and Bacon, 1977
Buku Teks
Pickle, Hal B.
Goodyear Publishing Company, Inc., 1972
Buku Teks
Crabbe, Ernest H., author
South-Western Publishing, 1951
Buku Teks
Crabbe, Ernest H., author
South-Western Publishing, 1961
Buku Teks
Kriz, Joseph A.
McGraw-Hill , 1973
Buku Teks