The BTN opens and you call in the BB (you are OOP).
You act first (OOP), so the default is to check and respond to the opponent's c-bet. Example: pot 5.5bb. On a K♠ 8♦ 3♣ board, 88 goes x/r, K7 goes x/c, and Q5 goes x/f. Against a second barrel on the turn, continue only with top pair or better.