unknown

The exact date when the ancient pyramids were built is still unknown to scientists.

(Chinese) 古代金字塔建造的确切日期对科学家来说仍然是个谜。

He was an unknown actor until he got the lead role in the famous movie.

(Chinese) 在获得那部著名电影的主演机会之前，他还是个默默无闻的演员。