Human geography : issues for 21st century
Peter Daniels [and others]
Prentice-Hall, 2001
 Buku Teks
2020 vision health in the 21st century
National Academy Press, 1996
 Buku Teks
Friis, Robert H.
Occupational health and safety for the 21st century
Jones &​ Bartlett Learning, 2016
 Buku Teks
Harrington, Rick
Stress, health and well-being: thriving in the 21st century
Wadsworth and Cengage Learning, 2013
 Buku Teks
Issues in health care management
edited by Steven Spirn and David W. Benfer
Aspen Systems Corporation, 1982
 Buku Teks