Water and Air Pollution. (2013). The History Channel website. Retrieved 3:32, May 22, 2013, from http://www.history.com/topics/water-and-air-pollution.
Water and Air Pollution. [Internet]. 2013. The History Channel website. Available from: http://www.history.com/topics/water-and-air-pollution [Accessed 22 May 2013].
“Water and Air Pollution.” 2013. The History Channel website. May 22 2013, 3:32 http://www.history.com/topics/water-and-air-pollution.
“Water and Air Pollution,” The History Channel website, 2013, http://www.history.com/topics/water-and-air-pollution [accessed May 22, 2013].
“Water and Air Pollution,” The History Channel website, http://www.history.com/topics/water-and-air-pollution (accessed May 22, 2013).
Water and Air Pollution [Internet]. The History Channel website; 2013 [cited 2013 May 22] Available from: http://www.history.com/topics/water-and-air-pollution.
Water and Air Pollution, http://www.history.com/topics/water-and-air-pollution (last visited May 22, 2013).
Water and Air Pollution. The History Channel website. 2013. Available at: http://www.history.com/topics/water-and-air-pollution. Accessed May 22, 2013.