Nasional Geographic, 2009
Buku Teks
Yang, Bo, author
Allen & Unwin, 1992
Buku Teks
Dobelstein, Andrew W., author
Wadsworth, 2003
Buku Teks
Huls, Erica, author
LEMMA B.V., 2001
Buku Teks
Dobelstein, Andrew W., author
Thomson Brooks/Cole, 2003
Buku Teks