空气中充满了微小的灰尘颗粒。

The air was thick with tiny dust ___particles.

该过程将材料研磨成微观颗粒。

The process grinds the material into microscopic ___particles.

在显微镜下，我们观察了每一个单独的微粒。

Under the microscope, we observed each individual ___particle.