ESCAP , {s.a}
Majalah, Jurnal, Buletin
Weeks, John R. (John Robert), 1944-, author
Cengage Learning, 2016
Buku Teks
Otero, George G., author
University of Denver, 1981
Buku Teks
Zelinsky, Wilbur, author
Prentice-Hall, 1966
Buku Teks
Gulati, P., author
Tata McGraw-Hill, 1984
Buku Teks