Artikel Jurnal
The Free Press of Glencoe, 1960
Buku Teks
Clason, W. E., 1898-, author
Elsevier, 1962
Buku Referensi
Clason, W. E., 1898-, author
Elsevier Scientific Publishing, 1976
Buku Referensi
Collier, Leonard Dawson, author
St. Paul's House Warwick Lane, 1973
Buku Teks