鲸鱼的鳍和人类的手臂是同源结构，都起源于相同的祖先。

The whale's flipper and the human arm are ___homologues originating from the same ancestor.

戊烷是甲烷的同系物，只是碳链更长。

Pentane is a ___homologue of methane with a longer carbon chain.