Germans introduce poison gas. (2013). The History Channel website. Retrieved 6:15, June 19, 2013, from http://www.history.com/this-day-in-history/germans-introduce-poison-gas.
Germans introduce poison gas. [Internet]. 2013. The History Channel website. Available from: http://www.history.com/this-day-in-history/germans-introduce-poison-gas [Accessed 19 Jun 2013].
“Germans introduce poison gas.” 2013. The History Channel website. Jun 19 2013, 6:15 http://www.history.com/this-day-in-history/germans-introduce-poison-gas.
“Germans introduce poison gas,” The History Channel website, 2013, http://www.history.com/this-day-in-history/germans-introduce-poison-gas [accessed Jun 19, 2013].
“Germans introduce poison gas,” The History Channel website, http://www.history.com/this-day-in-history/germans-introduce-poison-gas (accessed Jun 19, 2013).
Germans introduce poison gas [Internet]. The History Channel website; 2013 [cited 2013 Jun 19] Available from: http://www.history.com/this-day-in-history/germans-introduce-poison-gas.
Germans introduce poison gas, http://www.history.com/this-day-in-history/germans-introduce-poison-gas (last visited Jun 19, 2013).
Germans introduce poison gas. The History Channel website. 2013. Available at: http://www.history.com/this-day-in-history/germans-introduce-poison-gas. Accessed Jun 19, 2013.