宇航员必须小心太空中的微陨石，因为它们可能损坏航天器的表面。

Astronauts must be cautious of ___micrometeoroids in space as they can damage the spacecraft's surface.

每天晚上都有无数微流星体在大气层中燃烧，形成美丽的流星。

Every night, countless ___micrometeoroids burn up in the atmosphere, creating beautiful shooting stars.