50nl - AA faces river donk

[ddrstel]

No reads. Call or fold?

Full Tilt Poker - No Limit Hold'em Cash Game - $0.25/$0.50 Blinds - 6 Players - (LegoPoker Hand History Converter)

SB: $49.50
BB: $164.60
UTG: $48.50
MP: $50.00
CO: $67.50
Hero (BTN): $49.25

Preflop: Hero is dealt A[img]/images/graemlins/club.gif[/img] A[img]/images/graemlins/heart.gif[/img] (6 Players)
3 folds, <font color="red">Hero raises to $1.75</font>, SB folds, BB calls $1.25

Flop: ($3.75) K[img]/images/graemlins/spade.gif[/img] 5[img]/images/graemlins/club.gif[/img] 9[img]/images/graemlins/club.gif[/img] (2 Players)
BB checks, <font color="red">Hero bets $3.00</font>, BB calls $3.00

Turn: ($9.75) 8[img]/images/graemlins/heart.gif[/img] (2 Players)
BB checks, <font color="red">Hero bets $7.00</font>, BB calls $7.00

River: ($23.75) 7[img]/images/graemlins/heart.gif[/img] (2 Players)
<font color="red">BB bets $23.75</font>, Hero...?