Richards, Tom, author
Addison-Wesley Pub. Co., 1989
Buku Teks
Foster, Gerard N., author
Macmillan, 1994
Buku Teks
Fleming, Ian, author
John Wiley & Sons, ", 1976
Buku Teks
Scaife, Laura, author
Routledge, 2017
Buku Teks
Patterson, George N., author
International Studies Group, 1966
Buku Teks