AA on 4card straight board

[yundmi]

Villain is 39/11/.6 over 70 hands

PokerStars No-Limit Hold'em, $1.00 BB (8 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

BB ($72.65)
Hero ($108.80)
UTG+1 ($62.50)
MP1 ($67.65)
MP2 ($136.60)
CO ($100)
Button ($78.10)
SB ($6.50)

Preflop: Hero is UTG with A[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/club.gif[/img].
<font color="#CC3333">Hero raises to $4</font>, UTG+1 calls $4, <font color="#666666">6 folds</font>.

Flop: ($9.50) 7[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/spade.gif[/img], 2[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $8</font>, UTG+1 calls $8.

Turn: ($25.50) 5[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $20</font>, UTG+1 calls $20.

River: ($65.50) 6[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero???

Villain only has approximately 31 dollars left at this point. Are we check folding/check calling/shoving? If so, why?