宇宙中有很多神秘的现象。

There are many mysterious ___phenomena in the universe.

极光是一种令人惊叹的自然现象，科学家们一直在研究它。

The aurora is one of the most fascinating natural ___phenomena studied by scientists.

极光是一种令人惊叹的自然现象。

The aurora is a stunning natural ___phenomenon.