Perrin, Porter G.
Glenview, 1968
Buku Teks SO
Oxford university press , 1992
Buku Teks
edited by Della Thompson
Oxford University Press, 1996
Buku Referensi
Fowler, H. W. (Henry Watson), 1858-1933
At The Clarendon Press, 1954
Buku Teks
Hornby, Albert Sydney
Oxford University Press, 1984
Buku Referensi