Soltau, Roger H.
Longmans, Green , 1951
Buku Teks
Soltau, Roger H.
Longmans, Green , 1960
Buku Teks
Dyke, Vernon van, author
Nelson, 1992
Buku Teks
Laski, Harold J., author
George Allen and Unwin, 1960
Buku Teks
Russett, Bruce, author
Wadsworth, 2010
Buku Teks