Levinson, Charles, author
George Allen & Uniwin, 1972
Buku Teks
Sutcliffe, J.T., author
Macmillan, 1967
Buku Teks
Grunwald, Joseph, author
Bookings Institute, 1985
Buku Teks
Root, Franklin R., author
South-Western Publishing, 1978
Buku Teks
Meynaud, Jean
Methuen , 1967
Buku Teks