de / het
Many nouns are introduced without using a definite article, so the learner does not know, whether it is a de-word or a het-word. The rules for deciding "de" or "het" are complicated and have a lot of exceptions. Of course, as a native German speaker I can't complain, but I think it would be very helpful, if the "de " or "het" were always shown, in the overview of the lessons and in the translation of the words in the single questions as well.
It's a good idea. Something I usually do when in trouble with eng-to-nl translation exercises is to hover my mouse over the definite article: the first dutch article shown in the hint list is always the right one.
If you want, there is a whole website (and app) to help you with this: https://www.welklidwoord.nl/. You enter the word, it tells you the article. Easy-peasy!