'Det er' must be more like an impersonal phrase, (we have this in Swedish), so it is not conjugated; probably because the verb is never conjugated according to person/plural, so the connection diminishes. But in English, of course, it still has to be 'They are'. -- I suppose your sentence is not wrong, but another alternative. But in Swedish it would not sound as idiomatic, we prefer 'Det er', maybe the Danish do the same.
Thanks! that's very helpful. I thought they might have made a mistake or something until I read your post. That ended my confusion.
I'm also curious how learning Danish is for someone from Sweden (as I was surprised to find it's close enough I can read Swedish recipes to my wife. This was an added benefit I wasn't expecting:) There is a huge amount of similar vocabulary.
It is always hard to understand when a direct translation results in a grammatically incorrect sentence in the language which is being translated into. Word order is one thing, but in instances like this I hope Duolingo will --as they move out of beta-- find a way to let people know when this type of sentence is being offered. :)
If you where talking about 1 rabbit, pointing at it, then you say 'Den er min'. In this sentence there are several rabbits. It could be 'De er mine', but in this case the neutral beginning is used "Det er ... ", we have it in Swedish as well, without reference to the specific noun that follows. Other languages has to conjugate, where we don't.