You're right, this is confusing, because there is no context to give any clue.
With context: - "J'ai reçu cette lettre" (I received this letter) - "C'est de qui ?" (whom is it from? = who sent it?)
Another context: - "J'aime cette chanson" (I like that song) - "C'est de qui ?" (whom is it by? = who wrote it?)
You asked the right question with "how it works":
Preposition "de" often introduces adjuncts giving complementary information like origin, material, content, possession, purpose...
"c'est de qui ?" can refer to 2 variants of origin:
- cette lettre est de qui ? = whom is this letter from? (who wrote it? who sent it?)
- cette oeuvre est de qui ? = whom is this work by? (who made it?).
Prepositions are very tricky in both French and English because they are fickle, can have multiple interpretations, can be arbitrary and generally don't match from one language to the other.
As always with Duolingo, you are proposed sentences without context and you generally cannot guess if the translation will be direct or not.
Please accept to fail, redo your lessons as many times as necessary until they print into your brain, come back to earlier lessons once in a while to see how much you remember and you may find out that you are doing much better than you thought you would.
Dear Sitesurf! I am really appreciating your talent and sweet heart, you helps a lot to us. Still I would like to express my understanding, which is opposit to your advice. It is not like you repeat, repeat and the "thing" going to print into the brain. Brain is not a stone. Brain need emotions, mainly positive emotions, to take something into the memory. Without positive feelings the brain doesn't accept to store, or will block later the contains in live situations. So my humble advice to DL to use differently this kind of expressions. At least as you did, give some examples (in bracelets). Thank you again for your kindness. GNd
"De" has several interpretations and in the case of a child, "de" can express possession or origin because it is possible.
In the case of a piece of art, you can also ask "de qui est ce tableau ?" to get the painter's name, but "à qui est ce tableau ?" to know who the owner is.
In the case of a present one has received, you can ask "de qui est ce cadeau ?" to know who sent it and "à qui est ce cadeau ?" to know who the receiver is.
Sitesurf, I know this has been said MANY times on different threads, but I need to thank you for all the help you've been giving. Each time I find a word or sentence I don't understand, I look here and find you always answer my question (and obv everyone else's)! Thank you for making this learning experience even better :)