彩虹是一种美丽而罕见的自然现象。

A rainbow is a beautiful and rare natural ___phenomenon.

这位小音乐家六岁就能演奏肖邦的复杂曲目，真是个神童。

The six-year-old musician playing Chopin's complex pieces is truly a ___phenomenon.

短视频应用最近几年成为一种全球现象。

Short video apps have become a global ___phenomenon in recent years.