Agreed, all valid options should definitely be covered. I wonder if correctness is judged on sentence or word level? In the first case you would quickly get a large number of sentences to check against, but in the second case you would maybe get issues with some combinations being valid and some not. Anyway, hope we don't have to play the guessing game for long :)
I have the same problem. While it might be difficult to cover every possibility or convey the meaning given all the differences between Finnish and English and lack of context, the answers should at least be consistent.
A few lessons ago, in a very similar sentence (featuring a different animal), my "... grows fast" was corrected to "... grows quickly". Here it was just the opposite. Hope it gets fixed soon :)
As a native English speaker, this sounds off. Although 'fast' is both an adjective and an adverb it is more commonly used as an adjective, while 'quickly' would be a stronger choice as the adverb. "The fast car moves quickly."
It gives me the same feeling when someone uses the word 'good' as an adverb instead of 'well.'
As AgnusOinas points out, the translation "The small koala grows fast" is but one possible variant for this sentence. You need to allow for variation in all answers, not least because, at the moment, these answers give a very restrictive/prescriptive view of Finnish and because the same thing can be expressed in English in multiple ways (in this example, definite vs. indefinite article, present vs. continuous present tense). To reject the word "quickly" is incomprehensible. These things – and in particular a more accepting approach to word order in both languages – really need to be fixed to properly reflect the full scope of Finnish.
We are adding new possible translations all the time. We didn't intentionally reject "quickly" here, it just hadn't been added to the accepted translations yet. Just report anything that you find should be accepted but wasn't. There are a lot of possible translations that we just didn't think of yet! This course is still in beta and one of the reasons for this beta phase is to collect and add a lot of missing alternative translations.
Thanks for your answer. I get that this is a beta version and still something of a work in progress, and I don't mean to criticise unduly. It's great that there is finally a Finnish course on Duolingo (my mum has been waiting for this for years), but it's important that the list of acceptable answers accurately reflects the spectrum of possibilities, especially when translating into English. Having looked through a random selection of the classes, the most acute matter to address seems to be making sure both definite and indefinite articles in English are accepted (where appropriate) and that there are both present and continuous-present tense versions for all example sentences (where appropriate). Thanks and keep up the good work!