What?

[Disconnected]

The size of the donk bet worries me somewhat, but I'd be willing to get it in here. I assume an unknown would raise AK, AA, and 99 preflop to punish the limper, and would just as likely checkraise the remaining strong made hands that he would have limp/called (not that an unknown always does it, but that would be my expectation). I would call for a couple reasons: keep the donk behind you in the pot and encourage CO to bet again on the turn with a worse hand.

This is a tough spot, though. Folding has to be a pretty viable option (if not the best option).