森林中突然的不自然寂静让徒步者们感到紧张。

The sudden ___unnatural silence in the forest made the hikers nervous.

动物生活在不自然的环境中，并且早逝。

Animals live in ___unnatural conditions, and die early.

人工照明为植物创造了一个不自然的环境。

The artificial lighting created an ___unnatural environment for the plants.