How to abbreviate Pen Down?

The ways to abbreviate Pen Down.

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Pen Down
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APASmart Define. (2016). Pen Down. Retrieved December 4, 2016, from http://smartdefine.org/pen_down/abbreviations/a
ChicagoSmart Define. 2016. "Pen Down" http://smartdefine.org/pen_down/abbreviations/a (accessed December 4, 2016).
HarvardSmart Define 2016, Pen Down, Smart Define, viewed 4 December, 2016, <http://smartdefine.org/pen_down/abbreviations/a>.
MLASmart Define. "Pen Down" 8 June 2016. Web. 4 December 2016. <http://smartdefine.org/pen_down/abbreviations/a>