这条路似乎通往未知的地方。

This path seems to lead to the ___unknown.

这个遥远的小岛上生活着许多未知的生物。

Many ___unknown creatures live on this remote island.

这位歌手曾经是个默默无闻的新人。

The singer was an ___unknown newcomer at first.

在这个方程中，y代表未知数。

In this equation, y represents the ___unknown.