Runyon, Kenneth
Charles E. Merrill Publishing, 1982
Buku Teks
Dennis Adcock, Ray Bradfield, Al Halborg, Caroline Ross
Pitman Pub, 1993
Buku Referensi
Davies, Anthony H., author
Heinemann, 1973
Buku Teks
Chaffey, Dave, 1963-
Pear Education, 2012
Buku Teks
MacNamee, Brian
Routledge, 1995
Buku Teks