Oxford reference
Oxford University Press, 1990
Buku Referensi
Jelley, Herbert M., author
McGraw-Hill, 1985
Buku Teks
Gerstenberg, Charles W., author
Prentice-Hall, 1959
Buku Teks
Gerstenberg, Charles W., author
Prentice-Hall, 1951
Buku Teks
Gerstenberg, Charles W., author
Prentice-Hall, 1956
Buku Teks