Robert Cornraads and five outhers, author
Reader's Digest, 2015
Buku Referensi
Armstrong, Karen, author
Harper Perennial, 2005
Buku Teks
Engelmann, Karen, author
Harper Collins, 2012
Buku Teks
Armstrong, Karen, author
Alfred A. Knopf, 2000
Buku Teks
Rascati, Karen, author
Wolters Kluwer , 2014
Buku Teks