By / handled by / made up of (由)

Structure 由 + agent + verb （/ 由 + parts + 组成）

由 (yóu) introduces WHO is in charge of something or what it’s made of. (1) Responsible for an action: 这件事由你决定 = "you decide this". 这次会议由王经理主持 = "the meeting is chaired by Mr. Wang". (2) With 组成/构成, the parts that make up a whole: 这个小组由五个人组成 = "the group is made up of five people". It’s formal in register.

Examples

这zhè件jiàn事shì由yóu你nǐ决jué定dìng。
You’re the one to decide this.
这zhè次cì会huì议yì由yóu王wáng经jīng理lǐ主zhǔ持chí。
The meeting is chaired by Manager Wang.
这zhè个ge小xiǎo组zǔ由yóu五wǔ个ge人rén组zǔ成chéng。
The group is made up of five people.

Levels are indicative: they follow the standard Chinese Grammar Wiki (AllSet Learning) progression, not an official HSK 3.0 mapping. We never assign levels by eye.

This point and the other 370, with audio on every example, inside Wanyu.