"Succede in diverse ore della notte."
The answer given 'It happens in various hours of the night.' does not really mean anything in English. Could it be 'It happens at different times each night 'or 'It happens at different times in the night' English people do not say 'in various hours'
Please Duolingo do you have anyone English to proof read and comment on your English sentences?
Hi David1945, Thanks for pointing this out! We do have plenty of native speakers but a lot of sentences to keep track of so we always appreciate our members' feedback on strange gems like this one. The sentence has now been fixed. Thank you for your comment and in the future I would recommend using the "Report a Problem" button during the lesson to make sure things like this get sent to the right people on our team :)
Here's a link to a blog post about our data-driven approach: http://blog.duolingo.com/post/41960192602/duolingos-data-driven-approach-to-education and also more information on a recent study done on the effectiveness of Duolingo: http://duolingo.com/#/effectiveness-study