💡 Detailed Explanation
The correct choice is Option 3: 'Write down desired destinations on paper.' The woman suggests: 'じゃあ、まずお互いに行きたい場所を3つずつ紙に書いてみない？' (Well, first, why don't we write down three places we want to visit on a piece of paper?). The man agrees ('それがいいね'). Hotel and train bookings (Options 1 and 2) are already completed ('ホテルと新幹線はもう予約した'). Consultation (Option 4) will happen after they write down their choices. Thus, writing down the places is the next immediate task.