Eckersley, C. E. (Charles Ewart), 1892-1967, author
Longmans, Green and Co., 1953
Buku Referensi
London; Cassell LTD., 1978
Buku Referensi
Cuyas, Arturo, author
Appleton-Century-Crofts, 1962
Buku Referensi
by John W. McConnell [and others]
Scottforesman , 1990
Buku Teks
Cronin, Jeremiah A., author
Addison-Wesley, 1967
Buku Teks