[publisher not identified], [date of publication not identified]
Buku Teks
Lester R. Brown...[et all.]
W.W Norton, 1990/1995
Buku Teks
Dodd, Walter Fairleigh, 1880-1960, author
Century, 1923
Buku Teks
Hall, Rodney, author
Macmillan, 1998
Buku Teks
Hasluck, Nicholas, author
Penguin Books, 1987
Buku Teks