"Bears sleep in the winter."
Translation:Bjørne sover om vinteren.
From what I can tell, if 'in' and 'during' are interchangable, then om is used. Don't take my word for it though, I'm still learning too and this is just from what I've observed.
Oh, I just saw it on the tips and notes. I had forgotten to look at them before this lesson.
I think, it's because the bear does it (sleeps in the winter) on the regular basis