I recall reading elsewhere on another board that while we will as a matter of course use 's for statements of possession - "dad's hat," "dad's day in the sun," etc. - we will not find that Duolingo will accept 's for contractions, as in dad is --> dad's. I do not believe that this will change anytime soon.
I guess what that means - they have some accepted contractions that are automatically generated. This can create problems occasionally, the one I've ran into is when 's is accepted for has where it doesn't fit. It's obvious why the contraction for "is" won't be accepted automatically... But as far as I know the Russian team could add it manually if they want to.
Thanks very much to both of you (Ruth and Theron) - interesting points. I'm here to learn Russian, not English, so I'm personally quite OK about having to adjust to any understandable limitations like this. I'll get to learn the sense of the Russian sentence anyway, but just a very little bit later. But if there is more scope for alternative but correct English translations, it would make it that bit more comfortable. For all of us. That`s why I posted. So thanks again for your insights.
I agree that there could be more flexibility to the translation, since 's in both written and spoken English are commonly accepted as natural and appropriate grammar (except in my teachers' formal papers!). Not having seen what the Duo database of sentences looks like, I'm hazarding a wild guess that each sentence (not just each word) has to be added manually, and that would be a lot of additions to make, considering how many translation variations they already have to input on what are pretty simple sentences. Again, just a guess, but if it is so, I could see how they would stick to non-contracted words for their own sanity. :) I understand and appreciate your reasons for posting. Be well.