风暴过后，灰尘开始沉降在屋顶和街道上。

After the storm, the dust began to ___settle on the rooftops and streets.

如果温度保持在冰点以下，雪很可能会沉降并形成坚固的一层。

If the temperature remains below freezing, the snow will likely ___settle and form a solid layer.

在老图书馆里，你常常可以观察到灰尘随时间沉降在书籍上。

In old libraries, you can often observe dust ___settle on the books over time.