Questions & Answers about Hvilke bøger vil du gerne låne på biblioteket?
Hvilke means which and is used when you are choosing from a set of things, especially plural nouns.
So:
- Hvilke bøger = which books
- Hvad = what
You would not normally say Hvad bøger here.
A useful comparison:
- Hvilke bøger vil du gerne låne? = Which books would you like to borrow?
- Hvad vil du gerne låne? = What would you like to borrow?
The first asks you to identify specific books; the second is more general.
Because the sentence is asking about books in general, in the plural, without saying the books.
Here are the forms:
- en bog = a book
- bogen = the book
- bøger = books
- bøgerne = the books
So:
- Hvilke bøger ...? = Which books ...?
If it were Hvilke bøgerne, that would be wrong here.