Mistake in Plurals
Test 4 contains an error: Die Mädchen trinken Milch: The girls drink milk, and not: The girl is drinking milk
The girl drinks milk. - Das Mädchen trinkt Milch.
The girls drink milk. - Die Mädchen trinken Milch.
I doubt there is an error in such a basic sentence, it would have been fixed years ago. So check thoroughly before stating that there is an error. Maybe take a screenshot next time?
Edit: seems like it's true, the best way to report that would probably be to click "my answer should have been accepted" right in the question, since that should raise attention of the contributors. But I'm sure somebody's already done that. It depends how much they check these reports with old trees like the German one.