"Το τρίγωνο έχει τρεις γωνίες. The triangle has three angles.
Το ορθογώνιο δεν έχει τρεις γωνίες. The rectangle does not have three angles.
Το τετράγωνο είναι ένα σχήμα. The square is a shape.
These all have "the" because they show a specific item. In other cases you may not need "the".
There would be a good idea, but I'm afraid there are sentences in which something wrong would turn out. Automatic changes are always a bit dangerous. I wish I could do something more for Duolingo than simply remark to "please add got". I was thinking of proposing an Italian version of the Greek course for instance, maybe with the help of my Greek friend Nikos who is soon going to end his Italian course here. I have good general linguistic competences, a thorough ancient Greek background and an acceptable level of understanding of modern Greek. Three years ago I took the B2 exam and I think I will try Γ1 in October, but apart from that I often read, listen and speak in Greek. My knowledge of Italian language is quite good, I would say excellent, if that wouldn't sound pretentious. The real problem would probably be the free time I could devote to this Italian localization of the Greek course, as I'm quite busy.
Automatic changes are always a bit dangerous.
Yes, we learned that the hard way, so now we do them one by one.
I wish I could do something more for Duolingo than simply remark to "please add got".
You do a lot, I always know when I see a post from you that it will be constructive, and that is a great aid.
Oh, yes we wish we could do Greek in another language. And there is so much in common between Italian and Greek.
My knowledge of Italian language is quite good,
I'm sure of that seeing how you handle other languages.
If the time comes when you have free time we'd be so lucky to have you do whatever you felt like doing.
Thank you for all you do now.