easy river fold vs unknown?

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Full Tilt Poker ($2/$4 Limit Hold'em) converter

Preflop: Hero is BB with 9[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/club.gif[/img].
MP2 calls, MP3 folds, CO calls, Button calls, SB folds, <font color="#CC3333">Hero raises</font>, MP2 calls, CO calls, Button calls.

Flop: (12.5 SB) [J[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/heart.gif[/img]] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">Hero bets</font>, MP2 folds, <font color="#CC3333">CO raises</font>, Button folds, Hero calls.

Turn: (8.75 BB) [J[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/heart.gif[/img], 2[img]/images/graemlins/heart.gif[/img]] <font color="#0000FF">(4 players)</font>
Hero checks, <font color="#CC3333">CO bets</font>, Hero calls.

River: (10.75 BB) [J[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/heart.gif[/img], 2[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/spade.gif[/img]] <font color="#0000FF">(4 players)</font>
Hero checks, <font color="#CC3333">CO bets</font>, Hero calls.