Hare, Ronald, author
Churchill, 1979
Buku Teks
by John G. Holt [and others]
Williams & Wilkins, 1993
Buku Teks
Flynn, John E., author
McGraw-Hill, 1966
Buku Teks
Browning, Carl H., author
Oxford University Press, 1937
Buku Referensi
Black, Jaquelyn G., author
John Wiley & Sons, 2008
Buku Teks