Powell, Derek
Harlow Longman, 1994
Buku Teks
Butler, B.C.M.
Longman Scientific & Technical , 1988
Buku Teks
Bennison, George Mills
Routledge, 2013
Buku Teks
Anderson, Franz E.
Burgess Publishing, 1979
Buku Teks
Camm, F. J., editor
George Newnes Limited, 1960
Buku Referensi