To block the opponent's potential line of 4 pieces and create a future winning opportunity, I choose column 3 because it's the only column where my opponent has two pieces and I have one piece, and it's also the column where I have the most pieces. However, since column 3 is not available, I will choose the next best option which is to drop my piece in column 4 or 5 or 6 to be in a better position to win in the future turns or to block the opponent. Considering the current state of the board and the available columns, column 0 seems to be a promising option as it can potentially create a line of 4 pieces in the future turns.