静脉将血液带回心脏。

___Veins bring blood back to the heart.

叶脉清晰可见。

The leaf ___veins are clearly visible.

这块木头的纹理中有些漂亮的深色条纹。

This piece of wood has beautiful dark ___veins in its grain.

这首诗带有一种忧郁的基调，让人陷入深思。

The poem has a melancholy ___vein that makes people reflect deeply.