Wright, Lyle H.
Huntington Library, 1978
Buku Referensi
Horner, Avril, author
Harvester Wheatshea, 1990
Buku Teks
LLoyd-Smith, Allan Gardner
Macmillan Press, 1989
Buku Teks
Hill and Wang , 1968
Buku Teks
Leech, Geoffrey N., 1936-, author
Longman, 1994
Buku Teks