！a certain同义词是some，后接名词单数，中文意思是，一定的某一

All great songs are informed by a certain sadness and tension.所有动听的歌曲无不弥漫着某种伤感和紧绷感。

Linking the proposals in a single package did have a certain logic.

把这些提议联系起来成为一揽子提议确有一定的道理。