The difference is for example; if you point out a woman (vrouw) to your friend, you are saying "woman, (or wife)" without being overly formal. If you are speaking with/about a woman boss or an older woman you would use "mevrouw" it's the formal version. Also mevrouw is used to mean mrs./ms. like when we write letters Mrs. Jane Smith, ... Mevrouw Jane Smith...
How do you differentiate between "is hearing" and "hears" ? "The woman is hearing us now" is marked wrong here.
Ineed, in the example "Ze slapen nu", the correc answer is: "They are now sleeping". Then, why "the woman is hearing us now" is not a valid answer here???
And here is explained why https://english.stackexchange.com/questions/150616/is-it-really-wrong-to-say-im-hearing
How would this sentence be written if "nu" were in the beginning of the sentence?