"What book did you write?"
Translation:¿Qué libro escribiste?
I put Cual. I didn't know the difference between cual and que - this is what I found online: Cuál means 'Which' (as in which one?), and is usually the right word to use when followed by 'to be', as in ¿Cuál es la pregunta? Qué is used when immediately followed by the noun, as in ¿Qué pregunta tienes? Cuál es la pregunta.
- ¿Qué + ser...?: asking for a definition
*¿Qué + sustantivo(noun)...?*: Which (noun)...
- ¿Qué + verbo...?: When you want to ask to ask a question and there isn't a discrete set of choices (this is where the what vs. which argument comes in)
- ¿Cuál + ser...?: any question where you're not asking for a definition (don't get caught up in what/which here)
- ¿Cuál + de...?: Which of...
- ¿Cuál + verbo...?: When you have a discrete set of choices.
¿Qué + ser...?
¿Qué es vino?: What is (the definition of) wine?
¿Qué + sustantivo...?
¿Qué vino quieres?: Which wine do you want?
¿Qué + verbo...?
¿Qué quieres hacer esta noche?: What do you want to do tonight?
¿Cuál + ser...?
¿Cuáles son tus vinos favoritos?: What/Which are your favorite wines?
¿Cuál + de...?
¿Cuál de estos vinos quieres?: Which of these wines do you want?
¿Cuál + verbo...?
Tengo dos vinos, ¿cuál quieres?: I have two wines, which do you want?
I'm not fluent by any means, but I wrote this up because I found these rules really helped me understand the difference between qué and cuál. I hope it doesn't contain any errors, but point them out if it does, and I hope that it helps! I highlighted the case that applies to this exercise. Check out my source for a more in depth look.
Try the following link. It is not as simple as "what" or "which" but "qué" is always used when followed by a noun. https://www.realfastspanish.com/vocabulary/que-vs-cual