unable to add System.speech reference in visual studio 2013

trying to add System.speech reference in studio 2013.. but not able to find speech extension in dialog box. enter image description here explain how to add correctly.. running windows 8.1

You're targeting Windows Phone 8.1. As far as I can tell, System.Speech is only supported by the desktop framework (either the full framework from v3.0, or the client profile from v4.0).

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