In the task it says den. Here in the comment section the above example suddenly says det. What now?
Yeah I would also like to know
what's wrong with the answer "Hva mener det?"
You use "mener" for having something in mind.
Hva mener du? (What do you mean?)
Correct. Your (AutumnWine) translation means What does it think?, as in what is its opinion? .