"Auch was passiert ist, kann bislang keiner genau sagen."
The English translation is convoluted. I think "So far nobody can tell exactly what happened" sounds better.
I'm beginning to get a bit annoyed. I have repeatedly done this level, and i can understand it, but the version I write is not accepted...grrrr. I put: also nobody can say so far just what has happened. It's not beautiful english, but it's better than duolingo's effort!
I agree with you, this lesson is very long and quite difficult to understand.