Stress marks would be nice, as it is sometimes difficult to determine stressed syllables from the robotic voice.
Sometimes these make me lie...another said "I don't drink beer". Sure, sounds like me)) XD XD XD
There's nothing wrong with the English answer you're writing. Duo sometimes allows contractions and sometimes doesn't allow them, and there's no reason for it. It's just not in the database, I imagine, and that's a mistake. It should be allowed, because "I don't smoke" is much more natural English.