Bissinger, Buzz
Random House, 1997
Buku Teks
Wedgwood, C.V. (Cicely Veronica), 1910-
The British Council by Longmans, Green, 1955
Buku Teks
Neville, Isdell, author
Erlangga , 2011
Buku Teks
Koch, Edward I., 1924- , author
American Management Association, 2007
eBooks
Garland Publishing , 1988
Buku Teks