"They are not yours."
Translation:Non sono le tue.
"Non sono le Sue" should also be accepted. I realize the polite ("Lei") form hasn't been introduced yet, but for those who already know it, it's an obviously correct answer. If it's confusing, it should be left out, or it should make no difference whether or not it's marked. But to count it wrong is incorrect, because it's very clearly right.
I think I just figured this one out after getting it wrong as well. The answers read: "Non sono le tuoi" and "Non sono le tue" In both sentences "le" is used, indicating the feminine, but the first sentence uses "tuoi" which is masculine. Therefore the genders do not match. Does that make sense? Anyone agree?
No, "non sono le tuoi" was NOT marked as a correct answer. The folks in the comments above (as well as myself) had chosen it as a possible correct answer in addition to "non sono le tue." From what I'm understanding from this thread, the others were confused as to why "non sono le tuoi" was an incorrect choice. After doing a little backtracking through my notes I came to the same conclusion that you did. If it were to be correct it should say "non sono i tuoi," NOT "non sono le tuoi" because the genders don't match. :)
I think the real query here is ''how do we know to choose the femenine rules?'' 'Loro non sono i tuoi' has been accpted with 'Non sono le tue' as another correct solution. There is no indication of masculine or femanine involement in the english meaning yet Duolingo often chooses the femenine over the masculine, but not always (I have come across this twice already). To answer this I think it is just trying to keep you on your toes, know all the answers, have them ready and guess which is write.