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nbcnews.com
Schmid, Randolph E. (4 October 2007). "Crows use tools to find food". NBC News. Diarkibkan daripada yang asal pada 10 March 2017. Dicapai pada 11 November 2016.
Vannini, Phillip; Jonathan Taggart (2013). "Voluntary simplicity, involuntary complexities, and the pull of remove: The radical ruralities of off-grid lifestyles". Environment and Planning A. 45 (2): 295–311. doi:10.1068/a4564. S2CID143970611.
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Schmid, Randolph E. (4 October 2007). "Crows use tools to find food". NBC News. Diarkibkan daripada yang asal pada 10 March 2017. Dicapai pada 11 November 2016.