I analyzed the board: my O pieces are at (5,4) and (4,3), and playing in column 4 will drop my piece into (4,4), stacking on my existing O in column 4. This move sets up both a vertical threat in column 4 (with O’s at row5 and row4) and a horizontal connection on row 4 (with O’s at col3 and col4) that can later be developed into a win. It also occupies a central column and doesn’t give the opponent an immediate win opportunity. Therefore, I choose column 4.