Nourse, Edwin G
The Brookings Institution, 1938
Buku Teks
Henry Holt and Co., 1934
Buku Teks
Holt, Edwin B. (Edwin Bissell), 1873-1946
Macmillan, 1974
Buku Teks
Bryce, Murray D., author
McGraw-Hill, 1965
Buku Teks
Moulton, Harold G., author
Brookings Institution, 1935
Buku Teks