"어디에서 하키를 해?"
Translation:Where do they play hockey?
This is an example of a recurring problem in the beta version. In Korean pronouns are often assumed based on context. As a result, one would usually omit them. In the question above, depending on the particular context (who is present? who is the question directed to? etc.), one could imagine different possibilities. Duolingo is only accepting "Where do they play hockey?", which is a fine translation given context. This particular question is in banmal, informal speech, so I would assume the speaker and the receiver both know each other well. I could ask my friend, "Where do you play hockey?". That's the answer I thought would be correct. If it was polite or formal, perhaps "Where do I play hockey?" as though I was asking an attendant at a gym or fitness center. These single sentences and questions often only accept the pronoun that has been entered into the system. Most Duolingo learners, perhaps, wouldn't care so much about this discrepancy. But I think it is important and useful to understand these subtleties in Korean. Yes, the above question is colloquial and natural, but is it helping language learners?
I feel you. To be honest, the original Korean sentence should contain "그들은"("그들은 어디에서 하키를 해?") since the translation is "Where do they play hockey?"
It is just a random sentence without certain context.
This course is still in beta, so I'm guessing that the people working on it just didn't account for every option. You can flag it to recommend alternate translations.
I personally think it's helpful that I can choose multiple pronouns because it really drives home the point that pronouns just aren't used very often in everyday speech.