15/30 it's checked to me, i'm obligated to bet!

[sososoapy]

15/30 cp, full game
CO is bad lag
BB is decent lag, views me as TAG.

hero opens with A [img]/images/graemlins/heart.gif[/img]K [img]/images/graemlins/heart.gif[/img] in MP, CO calls, folds to BB who 3-bets, hero 4bet, call call.

flop: K [img]/images/graemlins/club.gif[/img]T [img]/images/graemlins/heart.gif[/img]7 [img]/images/graemlins/spade.gif[/img]
checked to hero bet, CO calls, BB raises, hero call, CO calls.

turn: Q [img]/images/graemlins/diamond.gif[/img]
BB checks [img]/images/graemlins/confused.gif[/img], hero BETS!, CO calls, BB raises [img]/images/graemlins/crazy.gif[/img], opps, what now??.....

how many check this turn?