black to move, what is best move?

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i played that game earlier today. ended already.

Well, black is up a piece, but horribly behind in development.  Opening the efile with pxp with black's king uncastled might be survivable but I'm not sure why black would allow the white rook to get involved so easily.  So I'm actually looking at d4, nd5, and while black still needs to think how to finish development and get the king safe, things just don't seem all that dangerous.  White has only one minor piece usefully deployed so where is the attack coming from?  d3 & Ng5 will do nothing since after d6 the rook guards f7.  So how does white whip up an attack?  Say play goes d4, nd5, nf6, d3, d6, bg5, be7.  So what?  White still has nothing, and can't afford to trade more stuff.  I think black is just won and white can only win if black helps a lot.  

mmm d4?