layer

旧书上覆盖着一层厚厚的灰尘。

There was a thick ___layer of dust covering the old books.

大气中的臭氧层保护我们免受太阳有害射线的伤害。

The ___layer of ozone in the atmosphere protects us from the sun's harmful rays.

乳霜在皮肤上形成一层保护膜。

The cream forms a protective ___layer on the skin.