Morgan, Theodore, author
Prentice-Hall, 1950
Buku Teks
Cairncross, Alec, author
Butterworth, 1960
Buku Teks
Johnson, Alvin S., author
Hearh & Co., 1911
Buku Teks
Reynold, Lloyds
Richard D. Irwin, 1966
Buku Teks
Hague, Douglas C.
Longmans, Green and Co., 1955
Buku Teks