Translation:La grandega parko havas multajn etajn arbojn.
I'm perfectly aware of that. What I meant is that so far, until this unit, the verb "Havas" was only used to show ownership( a park is unable to own anything). On the other hand "Enhavas" was being used to express "thing(s) inside a something". Also notice that "Devas" has been used to express a need, and yes in English we can say: I have to go now. But this is not english and it seemed to me (until now as I said) that Havi, Enhavi and Devi are three very distinct verbs in esperanto. But I guess I'm wrong.
I understand what you mean. Obviously, there is nothing wrong with La grandega parko enhavas multajn etajn arbojn, but Duolingo forces us to do quite literal translations, hence my response. Nevertheless, I think that enhavas should be accepted in this case too.
Apologies if my previous reply sounded a bit condescended. :-)
Se la arboj estas ĉirkaŭ la parko, oni tamen povas diri ke la parko havas arbojn, kvankam ĝi ne enhavas la arbojn.