Wegmann, Brenda
Random House, 1985
Buku Teks SO
Cunningham, Sarah
Oxford University Press, 1994
Buku Teks SO
Cunningham, Sarah
Oxford University Press , 1994
Buku Teks SO
O`Connell, Daniel C.
Springer, 2012
eBooks
Blass, Laurie
McGraw-Hill, 1990
Buku Teks SO