Penn, John, author
Collins, 1983
Buku Teks
Crystal, David, 1941-, author
Cambridge University Press, 2005
Buku Teks
Thompson, Laurence C
University of Washinton, 1967
Buku Teks
Nguyen, Dinh-Hoa, author
Charles E. Tuttle Co., 1991
Buku Referensi
Poole, Peter A.
Cornell University Press, 1970
Buku Teks