Pigou, A.C. (Arthur Cecil), author
Macmillan, 1957
Buku Teks
Coons, Alvin E., author
Rand McNally, 1959
Buku Teks
Slavin, Stephen, author
Richard D. Irwin, 1991
Buku Teks
Morgan, Theodore, author
Prentice-Hall, 1950
Buku Teks
Cairncross, Alec, author
Butterworth, 1960
Buku Teks