Nadeau, Gerard
Holt Rinehart and Winston, 1964
Buku Teks
Trewartha, Glenn T., author
McGraw-Hill, 1954
Buku Teks
Coyle, J. D. (John D.), author
John Wiley & Sons, 1986
Buku Teks
Barnum, Susan R., author
Wadsworth, 1998
Buku Teks
Gilmore, Charles M., author
McGraw-Hill, 1981
Buku Teks