This is the 13636th most frequent Russian word.
неизвестны
"Unknown" or "not known."
In this sentence, 'неизвестны' is used as a predicate, describing the state of being unknown for the subject 'causes of this problem', demonstrating an adjectival usage in plural form in Russian.
Причины этой проблемы всё ещё неизвестны.
The causes of this problem are still unknown.
Here, 'неизвестны' is used in an interrogative construction, addressing the listener's knowledge about the rules of this competition, functioning as an adjective in predicative form.
Неизвестны ли вам правила этого соревнования?
Are the rules of this competition unknown to you?
In this clause, 'неизвестны' is used in a descriptive manner to express the ongoing status of the reasons, highlighting its role as an adjective with the meaning 'unknown.'