💡 Detailed Explanation
The key is the particle 'に' in 'この問題には' (to this problem). We need a verb that collocates with 'に' to mean dealing with a situation. '対処する' (to deal/cope with) perfectly fits here as '〜に対処する'. Other choices like '提出' (submit), '納得' (consent), and '混乱' (confusion) do not fit grammatically or contextually.