"Whose cups are these?"
Translation:Wessen Tassen sind das?
Your sentence is a correct sentence, but it is just not the same sentence. What you asked is "Whose are these cups?" while the German sentence translates into "Whose cups are these?" The meaning might be similar, but structurally very different.
"Dies" here is in the nominative and isn't declined. If you reversed it, you'd say "Dies sind ihre Tassen."
You would need to say something like "Sie haben diese Tassen" which takes a plural accusative ending. It's acting as an adjective modifying Tassen rather than the subject.
It's because in "Wessen Tassen sind das" ("whose cups are these"), "das" is acting as a pronoun, not an article.
"Das" can be both a pronoun (substituting a noun, like "that" in "That is good" = "Das ist gut"), and an article (accompanying a noun, like "the" in "The food is good" = "Das Essen ist gut"). "Die", on the other hand, can only be an article ("the") like in "The newspaper is good" = "Die Zeitung ist gut".
You couldn't say "Wessen Tassen sind die" the same way you can't say "Whose cups are the" in English.
I was confused because I knew that "die" can also be used a s a relative pronoun, not just an article. For example "Die Tassen, die uns gehören, sind dort." But you've clarified things for me. Thank you :-)
Yes, you are right! "die" can be a relative pronoun too, but it's just used for relative clauses, meaning "which", "that" or "who". Like in your example: "Die Tassen, die uns gehören, sind dort." = "The cups, which belong to us, are there".
Me too. I was informed at some point you would use 'das' before the subject had been introduced and the corresponding article after it (as in this case).
A previous question in this practice lesson had the combination "dieser Tassen" indicating that the sentence was in the Genitive case. So, on this question, I was certain it was "dieser" (Genitive) again......but obviously that is incorrect. Suggestion: it would be VERY helpful if the answer provided a one or two word explanation like "Genitive case" or whatever. I think that would decrease the number of questions asked when people have a wrong answer! :-)