Is there a reason we cannot use a reflexive here? I was taught that since the object cannot actually perform the action, then a reflexive should be used to represent a passive voice, as in "El parque se habia cerrado." I have used it in other translation in Duo lingo without any issue, and this time it was rejected. I do not think there is any difference, but before I report it can someone please tell me if it is inappropriate to use the reflexive
The sentence you propose is perfectly right, but you have to notice that the original English sentence: "The park had closed" is not passive and not reflexive, and Duolingo asks you to translate the original sentence. I think that is the reason why they do not give you the answer as right.
el parque se había cerrado was accepted 8/27/18
Duolingo should accept correct English and correct Spanish. It should not accept the grammar from one language used in the other language when it is not correct. I too, believe that the "se" is perfectly acceptable and perhaps even necessary in Spanish.