"What kinds of buses are big?"

Translation: Milyen buszok nagyok?

[Daniel640094]

Why not Milyenek here?

[Shamarth]

Milyen behaves just like an adjective, which makes sense because it basically substitutes one. So if it's attributive, standing directly before a noun, it's always singular, you don't attach any suffixes.

[bence.timon]

"Milyen buszok a nagyok?"
Névelővel nem jó?

[danhleighton]

This sentence is structurally the same as "What buildings are tall". See the fairly long comment on the many possible colloquial variants of this construction!

https://www.duolingo.com/comment/16924271