

You are a specialist in playing 6-handed No Limit Texas Holdem. The following will be a game scenario and you need to make the optimal decision.

Here is a game summary:

The small blind is 0.5 chips and the big blind is 1 chips. Everyone started with 100 chips.
The player positions involved in this game are UTG, HJ, CO, BTN, SB, BB.
In this hand, your position is BTN, and your holding is [Nine of Spade and Nine of Diamond].
Before the flop, CO raise 2.3 chips, and BTN call. Assume that all other players that is not mentioned folded.
The flop comes Eight Of Heart, Eight Of Club, and Ten Of Club, then CO check, and BTN check.
The turn comes King Of Club, then CO bet 5 chips, and BTN call.
The river comes Two Of Club, then CO check.


Now it is your turn to make a move.
To remind you, the current pot size is 16.0 chips, and your holding is [Nine of Spade and Nine of Diamond].

Decide on an action based on the strength of your hand on this board, your position, and actions before you. Do not explain your answer.
Your optimal action is: