How to abbreviate Pen Down?

The ways to abbreviate Pen Down.

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Pen Down
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APASmart Define. (2015). Pen Down. Retrieved February 7, 2016, from http://smartdefine.org/pen_down/abbreviations/a
ChicagoSmart Define. 2015. "Pen Down" http://smartdefine.org/pen_down/abbreviations/a (accessed February 7, 2016).
HarvardSmart Define 2015, Pen Down, Smart Define, viewed 7 February, 2016, <http://smartdefine.org/pen_down/abbreviations/a>.
MLASmart Define. "Pen Down" 7 June 2015. Web. 7 February 2016. <http://smartdefine.org/pen_down/abbreviations/a>