ferment

牛奶在温暖的环境中会发酵变酸。

Milk will ___ferment and turn sour in a warm environment.

新政策公布后，社交媒体上出现了一阵激烈的讨论。

There was a ___ferment of debate on social media after the new policy was announced.

多年的政治骚动最终爆发为一场全国性的抗议运动。

Years of political ___ferment finally erupted into a nationwide protest movement.