"민지가 강당에서 발표했어요."
Translation:Minji presented in the auditorium.
To present is a transitive verb in this sense (and generally, unless you're a pediatrician, just as to represent is unless maybe you're into hip-hop). I think "gave a presentation" would be more formal -- as this is informal speech I'm thinking "did a presentation" or "presented something" are about as close as you can get in proper English, but who speaks proper English anymore?
Both "to present" and "to announce" are transitive verbs. They need an object complement in order to make sense.
Your translation with 'it' as object makes the sentence acceptable. DLG's translation on the other hand is grammatically incorrect.
The alternative is to use either "to give a presentation" or "to make an announcement".
two things to this: it is not that free since you are constantly offered the possibility to pay - which I stoped doing when I realized I was paying for a service that is chocking for its low quality. They should have prepared this correctly before going public but they obviously prefered to hastingly put these classes online to get the adds (let's not be naive, they do get a lot of money for the content they put online so they just put online random things). But most importantly, and that is extremely chocking: the fact it is free should not be an excuse to mislead people with random lessons that teach mainly errors and inconsistencies. Whether the lessons are free or not: when you teach something, you have the responsability to not spread bullsh*** (it's the same principle than fake news).
I know not much on the internet is truly free, and that Duolingo is subscription- and ad-supported (...Although, on a PC web browser, you can use an ad-blocker and retain full functionality).
But you are going too far. The Duo people aren't doing anything like spreading propagandistic "fake news". The mistakes that Duolingo has are either quickly corrected, or so minor as to make little functional difference. Duolingo is a great language learning tool.
I would advise using Duolingo in addition to other sources, like a class, textbooks, YouTube, native speakers, and other online language learning tools (Memrise, FluentU, LingoDeer...). It's a mistake to think you can get everything in one place.
I am not going too far: they do spread a lot of mistakes and that they are still in place 1 (sometimes 2 years) later is not what can be called "quickly" corrected. Also there is not such things that is a minor mistakes (specially since there are some major mistakes still here, even though several Korean natives flagged them). Also you are talking about this "getting everything in on place", if your read thoroughly I never mentionned anything about that and no matter how many tools you use appart from Duolingo, Duolingo still teaches mistakes. If they consider some of them are not mistakes, they should at least have proper tips and notes. As far as Korean is concerned I- and the Korean teachers who went through duolingo with me - recommend to not use Duolingo until their team fixes which is obviously a draft (and for some of the other languages I tested, I would not recommend either to be honest). And as mentionned before, ad block or not, they still get paid with their ads (and with some of the learners who do still pay for the service) for teaching mistakes that they never fix. That is morally not acceptable. If you teach something to people, take responsibility for it: when you do something do it properly.
The mistakes on Duolingo are often just quibbling, i.e., no big deal. I haven't run into anything that is so fundamentally different in meaning that the question is completely useless. However, you are right that there are a few awkward sentences, in English and Korean, that still exist after years. And sometimes the answer they want is needlessly specific, yes.
I talked about multiple sources because it sounds like you're asking Duolingo to be your one perfect source for Korean language learning. If you broaden your search a little, then any mistakes you find here (even if they are as major as you say, which I disagree with), won't matter much in the long run.
In spite of its flaws, Duolingo provides a lot of value to many people. I will continue to take what I can from it.
My question is: if you think Duolingo is so terrible, why are you still here?