The first Earth Day. (2013). The History Channel website. Retrieved 5:51, May 19, 2013, from http://www.history.com/this-day-in-history/the-first-earth-day.
The first Earth Day. [Internet]. 2013. The History Channel website. Available from: http://www.history.com/this-day-in-history/the-first-earth-day [Accessed 19 May 2013].
“The first Earth Day.” 2013. The History Channel website. May 19 2013, 5:51 http://www.history.com/this-day-in-history/the-first-earth-day.
“The first Earth Day,” The History Channel website, 2013, http://www.history.com/this-day-in-history/the-first-earth-day [accessed May 19, 2013].
“The first Earth Day,” The History Channel website, http://www.history.com/this-day-in-history/the-first-earth-day (accessed May 19, 2013).
The first Earth Day [Internet]. The History Channel website; 2013 [cited 2013 May 19] Available from: http://www.history.com/this-day-in-history/the-first-earth-day.
The first Earth Day, http://www.history.com/this-day-in-history/the-first-earth-day (last visited May 19, 2013).
The first Earth Day. The History Channel website. 2013. Available at: http://www.history.com/this-day-in-history/the-first-earth-day. Accessed May 19, 2013.