A:
No you can not, there is no mic input in the D3100, that would be in the D7000. You could though use an external recording device like the Zoom H4N and sync in post production, which instead of a mini mic input you get pro XLR with many other controls and features than what a camera would have. Also if you have an assitant the Zoom would allow you better mobility and movement as you are not connected to camera.