The pronunciation leaves me a bout wanting. «le bol» sounded much too enunciated at the end, making it seem as if they were trying to say «le bolle». The ending phoneme was enunciated, which is really not how you do it, at least as far as I recall from my classes. It's tough to make it understandable, especially for varying levels of learners, so I get it, though.
You are not supposed to judge Duolingo against your class standards. Suppose your teacher was unnecessarily pedantic! I'm sure no one likes anyone who "speaks like a book."
Here, you go back to child level, and learn via immersion. Take it as you hear it. Then you can return to school and invent rules on enunciation. Primarily, you should be understood by native speakers, literate or otherwise.
Class textbook rules - numerous as they are - are why nobody ever acquires a language without actually listening to native users.