Spear, Percival
The University of Michigan Press, 1961
Buku Teks
Bradford, Frederick A.
Longmans, Green, 1932
Buku Teks
Rodgers, Raymond
Alexander Hamiltion Institute, 1962
Buku Teks
Thorne, W.J.
Oxford University Press , 1948
Buku Teks
Hobbs, Lisa
McGraw-Hill, 1967
Buku Teks SO