"Are those our oranges?"
Translation:Sind das unsere Orangen?
When you use “this/that” to introduce a thing, you almost always use das. Dies is okay, but significantly less common. If you add the ending -es, that sounds like “this one” (i.e. it sounds like you were already talking about things from the same category and now you’re pointing out a specific one). In this case maybe: “Hier sind vier verschiedene Getränke. Dieses ist Bier.” (Here are four different drinks. This one is beer.)
When we introduce something/someone using a formula such as “this is…” (also including the corresponding question “is this…”), the demonstrative pronoun is always singular neuter, regardless of the gender and number of the noun. So for example also: Das ist mein Mann. Not: *Der ist mein Mann. If you want you can think of it this way: Since the noun hasn’t been introduced yet, the gender and number are still undetermined, so we default to singular neuter.
To be sure, there are situations where der ist… etc. is correct, but only if the demonstrative refers back to a noun which has already come up before. For example: Komm dem Hund besser nicht zu nahe. Der ist gefährlich. “You had better not get too close to the dog. It’s dangerous.” Here der does not identify a new noun but instead refers back to the already established noun Hund, so it agrees with it in gender and number. In English you’d often use a personal pronoun (or if it’s singular “that one” instead of just “that”) in such a situation.
I’m not completely sure if the rule about using neuter singular to introduce nouns is in the Duden grammar (I’m afraid I don’t have one nearby right now) but if I were to grade a test I would definitely mark it wrong because it doesn’t feel grammatical to me as a native speaker.