Chengyu are idioms composed of four characters, and they make your writing look fancy. Read more about them, with lists of the most useful examples, in the following blog posts:
hackchinese: "Chinese Idioms: Common Chengyu for Daily Conversations"
https://www.hackchinese.com/blog/chinese-idioms-common-chengyu
FluentU: "Chinese Idioms: 34 Useful Chengyu to Improve Your Mandarin Fluency"
https://www.fluentu.com/blog/chinese/chinese-idioms-chengyu/
Mandarin HQ: "26 Chinese Idioms with Numbers"
https://mandarinhq.com/2022/04/chinese-idioms-chengyu-numbers/
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