Nårh!! Kan man ikke sige "Det skal være skjult" som svar på "It must be hidden". ??

Den må være gemt= i can't find it; it must be hidden. It has to be hidden (away, so the children don't find it)= det må gemmes.

Why is "Det må gemmes" not correct?

The more I think about this, it has two meanings, depending on context: I can't find it so someone must have hidden it = det må være gemt/skjult We don't want anyone to find it, so we have to hide it (which I find unusual, because it can be ambiguous [tvetydig]) = Den skal gemmes.

It has to be hidden

The direct translation of skal is shall. No longer common usage in Dansk?

Reported: "det skal være gemt" should be accepted.