Tengo que responder a su carta. My answer: I have to respond to their letter. Duolingo say Wrong, it's "I have to respond to HER letter." question, why and how do they know it can only be HER. Can't "su" refer to "his letter," or "their letter," as well as "her letter." I sent off a feedback stating my position. However, is their something I missed here; any reason I could be wrong?. if I am correct i am starting to find such things very discouraging.
I would have thought his/her/your/their were all correct. I agree this sort of thing can be very frustrating, but please remember they have a very small staff, most of whom are focussed on technical development.
Well, I thought so too, so this is frustrating for me. Apparently duolingo will also accept "your" but not "their". Found out after redoing. Thanks for answering.