这个地区每年的降雨量变化很大。

There is a significant ___variation in annual rainfall in this region.

这首歌有几种不同风格的变奏版本。

This song has several ___variations in different styles.

蝴蝶翅膀颜色的差异是自然选择的结果。

The ___variation in butterfly wing colors is the result of natural selection.