Coyle, William, author
Wadsworth and Cengage Learning, 2013
Buku Teks
Roth, Audrey J., author
Wadsworth, 1995
Buku Teks
Watson, George, author
Longman, 1987
Buku Teks
Meyers, Alan, 1945-, author
Pearson Education, 2014
Buku Teks
Rudestam, Kjell Erik
Sage Publications, 1992
Buku Teks