Freemantle 2006. Freemantle, Michael. Archives For Africa. American Chemical Society. Chemical & Engineering News. 2006-05-15 [2016-09-25]. (原始内容存档于2016-09-25). 引文格式1维护:日期与年 (link)
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Freemantle 2006. Freemantle, Michael. Archives For Africa. American Chemical Society. Chemical & Engineering News. 2006-05-15 [2016-09-25]. (原始内容存档于2016-09-25). 引文格式1维护:日期与年 (link)