Soltau, Roger H.
Longmans, Green , 1951
Buku Teks
Soltau, Roger H.
Longmans, Green , 1960
Buku Teks
Barnes, James F., author
St. Martin`s Press, 1980
Buku Teks
Laski, Harold J., author
George Allen and Unwin, 1960
Buku Teks
Laski, Harold J., author
MCML Yayasan Pembangunan, 1950
Buku Teks