"Whose bear is it?"
Translation:Hvis bjørn er det?
Because 'det' is used as the subject of være/blive when the predicate is a noun, a pronoun or an adjective, irrespective of gender and number.
In this sentence, "it" is the subject. It becomes clearer as a statement: "It is my bear." = "Det er min bjørn"
I made this error, too. Though, I still don't really understand how it is Det over Den. The være/blive explanation doesn't mean anything to me i'm afraid as i've yet to get to anything where those words have cropped up. So how do I know to choose Det over Den when the word, as in this example, is an n-word? I know you say that 'it' is the subject, but i still don't get how you're supposed to figure out which word for 'it' you use in this context.
I can't remember specifics, but i know i've come across other phrases where I've used one and it's said the other was also an acceptable answer, as well. Also, in the one of the early notes for den/det it mentions 'depending on grammatical gender of the subject, but as a rule det is for inanimate objects', which bears are not.
Sorry if i'm being dense. I'm better at understanding by examples as i don't always truly understand all the academic wording when talking about language.
At være means to be, so er is a conjugation of at være.
"It" is the subject of the sentence (which is a sentence with være and a predicate), and it therefore has to be "det".
You can think so that you ask "hvad er det?", as you cannot know whether it will be an "en" or "et" word. Then you begin your answer with the same word "det er..." If you know German, you can notice that the idea is the same: you have to ask "Was ist das?", and then answer "das ist ein Bär", even though it is "der Bär" (a masculine), and "das" is in fact the neuter article. (In the Scandinavian languages, "det" is the neuter article; the old German masculine and feminine genders have merged to a common gender form "den".)