Lindberg, Jordan J., author
Mayfield Publishing Company, 2001
Buku Teks
Rae, John B., author
McGraw-Hill, 1949
Buku Teks
Keegan, John, author
Routledge, 1996
Buku Referensi
Sharma, S.R.
Orient Longmans Ltd, 1951
Buku Teks
Palmer, Alan, author
Routledge, 1996
Buku Referensi