Castel, Helene
Macmillan, 1971
Buku Teks
edited by Joel J. Lersier
Englewood Cliffs, N.J., Prentice-Hall
Buku Teks
Debenham, Frank, author
Reader's Digest Association, 1979
Buku Referensi
London : Raeder's Digest
Majalah, Jurnal, Buletin
Macmillan, 1971
Buku Teks