HSK 5 HSK V4
Correct

在于

/ zàiyú /
Strokes

Definition

to be in/to lie in/to consist in/to depend on/to rest with

Example

As a Verb

lie in; consist in

1
Zhànzhēng
战争
de
目的
zài
在于
xiāomiè
消灭
zhànzhēng
战争
  

The aim of war is to eliminate war.

2
Xìng
幸福
zài
在于
zhī
知足
  

Happiness consists in contentment.

As a Verb

depend on; rest with; be determined by

3
zài
在于
  

It's up to you to decide whether to go or not.