"Která věta je správně?"

Translation: Which sentence is correct?

[bright_flash]

Why do we use správně here and not správná?

[kacenka9]

Both answers are accepted when translating to Czech. The správně version is an adverb while správná is a pronoun. The nuance in meaning is very small.

[endless_sleeper]

Správná is a feminine adjective, definitely not a pronoun ;)