这片森林的树木极为密集，几乎看不到阳光。

The ___densest part of the forest is too dark to see sunlight.

这篇文章太晦涩难懂了，我需要读好几遍才能理解。

This article is the ___densest one I've ever read; I need to go through it several times to understand.

尽管老师重复了五遍，他仍然是全班理解得最慢的学生。

After the teacher repeated it five times, he was still the ___densest student in the class.