Enger, E. D., & Smith, B. F. (2006). Environmental science: A study of interrelationships (10th ed.). McGraw-Hill College.

Enger, Eldon D., and Bradley F. Smith. Environmental Science: A Study of Interrelationships. 10th ed. New York: McGraw-Hill College, 2006.

Enger, Eldon D., and Bradley F. Smith. Environmental Science: A Study of Interrelationships. 10th ed. McGraw-Hill College, 2006.