Kaufmann, Christian
Basel Pharos 1972
Buku Teks
Reader's Digest Association.
Reader's Digest Association, 1968
Buku Referensi
Schanely, Leon E.
Universitas Cendrawasih, 1989
Buku Teks
Williams, F.E.
Oxford University Press, 1936
Buku Teks
Wilson, Lindsay
McGraw-Hill , 1975
Buku Teks