💡 Detailed Explanation
The correct choice is Option 3: 'Go put the taken-off socks into the washing machine.' Although the mother initially instructed him to put the toys away first, the son pointed out his dirty socks on the floor ('脱ぎっぱなしの靴下がここにあるよ'). The mother commands: 'じゃあ、それを先に洗濯機に入れてきて。そのあとでおもちゃをお願いね' (In that case, put that in the washing machine first. After that, do the toys). Therefore, the immediate first task is Option 3.