这些微生物太小，肉眼无法看到。

These microbes are too small to be seen with ___the ___naked ___eye.

金星通常非常明亮，在夜空中肉眼可见。

The planet Venus is often bright enough to be visible to ___the ___naked ___eye in the night sky.

在理想条件下，仙女座星系是肉眼能观测到的最远天体。

Under ideal conditions, the Andromeda Galaxy is the farthest object observable with ___the ___naked ___eye.