"I let the bear sleep."
Translation:Jeg lot bjørnen sove.
"Jeg lar bjørnen sove" would be a gramatically correct translation as well. Of course, the lesson is about past tense, but I think it would be better to specify it somehow in such cases
It's useful to suggest things like this because the strengthening exercises don't tell you the skill group from which a sentence was pulled (rightly so), and months later it would be an easy mistake to thing you're being asked for the present tense.