"Who does this girl love?"
Translation:Ez a lány kiket szeret?
It's just that kit is singular and kiket is plural.
The Hungarian sentence with kiket is implying that the girl loves multiple people, and the person who is asking wants to know who they are. With kit it would be just one person.
English doesn't have a "singular who" and "plural who" so it's impossible to tell from the English sentence alone whether kit or kiket is the correct thing to use. Both answers should be accepted.
"Whom" is textbook-correct but it is pretty uncommon to hear it in a simple sentence like this these days. It can sound jarringly over-formal in certain contexts, and judging whether or not to use it is more of a social question than a linguistic one. I do think that Duo should accept both, but I think their choice to present "who" as the correct answer here is reasonable based on current usage.
What I mean is, in an academic setting I would sound perfectly fine saying: "From whom did Teller initially get the idea for the fusion bomb?"
But if I am with friends in a casual setting and I ask, "To whom does this beer belong?" then I definitely run the risk of being punched in the arm for sounding pretentious.
In English, yes, both should be accepted.
"Whom" is slowly dying and many people use "who" in all situations, even those that call for the accusative case. Some older or more conservative speakers still consider this a mistake, but I think Duolingo accepts it.
But Hungarian doesn't have this simplification -- after all, cases are still alive there.
Similarly in German: nobody would think of saying "Wer liebt das Mädchen?" to ask about the object of the girl's love; it has to be "Wen liebt das Mädchen?"
You are mixing two things here.
"Who" is the object, the girl is the subject. There is no question about that. The girl is the one who loves somebody.
You are mixing it up with the complete opposite when somebody loves this girl: "Who loves this girl?"
They are totally different sentences.
- Who loves this girl = Wer liebt dieses Mädchen
- Who does this girl love = Wen liebt dieses Mädchen
- Whom does this girl love = Wen liebt dieses Mädchen
- Whom loves this girl = (not possible)
The first two sentences are different in English -- even for those speakers who use "who" for the accusative, the sentence order makes it clear whether you are asking about the subject or the object, because "do-support" is required when asking about the object and cannot be used when asking about the subject.
And you can't use Italian since I don't think it has separate nominative and accusative forms of chi.