Translation:Which piece of furniture is the frog sitting down on, the armchair or the shelf?
... yet it is correct!
The solution I was given is not natural, and just weird in English.
The problem is, English scentences such as this may be an adequate representation of the Hungarian text that help us to understand Hungarian grammar and sentence structure, but it is well nigh impossible to guess the correct answer. So we have to memorize bad English in order to answer correctly.
In my experience, this is the case for just about every language. There are certain things that just don't sound right when translated literally. It's not that bad in, say, French-to-English or Spanish-to-English because there are a lot more sentences that DO translate literally and there are regular rules for sentences that don't (e.g. "qu'est-ce que" always means "what", "il y a" always means "there is", etc.) For those types of sentences duolingo usually accepts both the literal translation and the best English one, and it's not too taxing on the developers. The problem I'm seeing with Hungarian is that there are FAR MORE sentences that make improper English when translated literally, and the developers seem to be straining to incorporate all possible correct translations. The flaw, I think, is in the design of the duolingo courses themselves. The most effective way to learn Hungarian would probably be to learn the "bad English" literal translation to understand how Hungarian uses its prepositions, as well as the correct English translation to understand what the sentence is actually saying for every sentence. One translation per one sentence can't accomplish this, and with the course being incomplete at this time it really just leads to confusion.
If they want the answer to be "sitting down" they need "le" in the Hungarian. Otherwise, there is no way to guess in the English translation if it is "sitting on" or "sitting down on".
------- i think that a shelf is usually built into the room, so a shelf wouldn't be a piece of furniture (although we certainly buy and install shelves ). second, the frog chooses or picks somewhere not to sit on but to land on . maybe if you had been chasing the frog around the room it would eventually choose a piece of furniture to sit down onto . . .
Also a shelf:
Since the days of Ikea, I'd say that most shelves are free-standing. All of the shelves in my flat are. :P
With your second concern you're correct, I think. The given sentence is okay in both languages, but not the most natural way to express it. Frogs do not "sit down", but they "jump" somewhere and then they "sit" there.