constituent|constituents

氧气是空气的主要组成部分之一。

Oxygen is an important ___constituent of air.

面粉是面包的主要成分之一。

Flour is one of the main ___constituents parts of bread.

牛奶的主要成分包括蛋白质、脂肪和乳糖。

The main ___constituents of milk are protein, fat, and lactose.