Griffiths, David J., author
Prentice-Hall, 1999
Buku Teks
Johnson, Kenneth D., author
The Benjamin, 1984
Buku Teks
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