I was going through a JLPT grammar practice book and am confused on a question:
「一郎、まだ起きているかな。」
「部屋の電気が消えているから、もう_____よ。」
I choose 寝そう since ~そう is often used to make conjectures based on visual info (Ichiro's light is off). But the answer key says 寝たよう is better. Any thoughts on why?