I had my answer rejected for writing "Birds can fly but they cannot swim"! From Oxford dictionary: "Both cannot and can not are acceptable spellings, but the first is much more usual." It seems like there are a lot of these types of errors in the Hindi Duolingo, but not in other languages like Spanish and French -- would be great to get them corrected!
This answer "Birds can fly but can not swim" is quite unnatural. How about "Birds can fly but not swim"?
I think the translation is fine, except for "can not" (which should be "cannot").
I think it's fine too, though someone might want to have a word with the ducks (swans, geese, gannets, puffins etc).
Sadly, they are not as versatile as the cats, who can both sit and fly.
I had the same, and it is annoying that it is not accepted - as if the real mistakes I make wouldn´t be enough ...