Translation:I do not believe that you were left alone.
I guess I'm still trying to tease out the implications here, which is not to say I'm not grateful for your help. It actually adds some new insights. It's just that the way they translate it sounds like, "I believe there were actually other people in the house, so I do not believe you were left alone." Whereas my translation was more along the lines of "Since you've always been afraid to stay alone, I do not believe that you stayed alone [this time]." Of course there are nuances in any translation, but could this Italian sentence be interpreted both ways?
The translation on the discussion page says, "I do not believe that you were left alone." The translation on the test page says, "I do not believe that you have been alone." My answer was, "I do not believe that you have stayed alone." And it was marked wrong. I've been wrong many times, and can usually learn from it. But without context, this is tricky to translate. I'm usually not picky about what Duo finds acceptable, but this is really not acceptable to me as a learner, because exactly what am I supposed to learn from this?