Charron, Helena S., author
W. B Saunders , 1998
Buku Teks
edited by Greta Thornbory
Wiley Blackwell, 2009
Buku Teks
edited by Derek Bingham
John Catt, 1989
Buku Referensi
Leedam, Elizabeth J., author
McGraw-Hill , 1972
Buku Teks
Falmer Press, 1985
Buku Teks