The use of "的“
First of all, it's great news that chinese is out! It's a very fascinating language. I've been learning it for about a year now. I took the chinese test and I got a couple of things wrong- the use of "的". I was taught (by chinese speakers) that we don't need to use it if the relationship between people ( eg. mother, father, wife, brother...) is close so 我妈妈， 我爸爸， 我哥哥， 我妻子 should be correct. To my surprise duolingo didn't accept this answer. So what's up with the "的"?
I've been to China and I've heard people drop the 的 in those situations. I think they just want you to get used to using 的 to show possession.
Perhaps, but I think it's because they didn't make it sense the situation (which would have been hard...)
Chinese course of Duolingo is still in Beta, so many right answers might not be added to the course yet :) You should report those sentences to them and suggest your answer, then they will review it and add it up! ^^
It's a mistake. Lesson notes (https://www.duolingo.com/skill/zs/Family-1) also mention that 的 can be skipped:
"For people that you have a close relationship with (e.g. family), and for institutions and organization you are involved with (e.g. work, school), you can choose to leave out the 的, but this only happens with pronouns."
I had the same problem a few minutes ago. Simply report all similar mistakes.
I believe it's because it's spoken. When my Chinese teacher speaks she omits 的， but not for writing. I could be wrong; but she has taught us some things that are written one way, and change when you speak them. Like 那 nà4 can become nèi.
I was taught that it's dropped even while writing. It's probably because- as Tamuna has written - it's still in beta.
Because the 的 is used usually in these situations, Duo can't tell. However, these days most Chinese speakers drop it, like me. You usually would, in fact, say 我妈妈 or 我家 and things like that. Duo isn't aware of this, and you can't blame the team for the course is still in Beta. Report it!