The fundamental unit of the hierarchy is the association .

等级系统中的基本单位是群丛。

AD. The thread is a fundamental unit of the operating system.

该线程是操作系统的基本单位。

According to linguistic theory, the word is the fundamental unit of language.

语言学理论认为，词语是构成语言本体的基本单位。

Sequences are the fundamental unit of interpretation in sequence stratigraphy.

层序是层序地层学解译的基本单位。

All living organisms are made of cells. The cell is the fundamental unit of life.

一切有机体都是由细胞构成，细胞是生命活动的基本单位。