Spear, Percival
The University of Michigan Press, 1961
Buku Teks
Brown, Joe David
Time Incorporated, 1961
Buku Teks SO
Hobbs, Lisa
McGraw-Hill, 1967
Buku Teks SO
Bradford, Frederick A.
Longmans, Green, 1932
Buku Teks
Rodgers, Raymond
Alexander Hamiltion Institute, 1962
Buku Teks SO