Taafe, Robert N.
Washington Frederick A. Praeger, 1965
Buku Teks
Taaffe, Robert N
Frederick A Preager, 1965
Buku Teks
Ward, Dederick C.
Scarecrow Press, 1981
Buku Referensi
Lieb, Robert C.
Reston Publ, 1985
Buku Teks
O`Neill, Robert
Longman, 1990
Buku Teks