3 sentences

1. 学习汉语需要掌握很多成语。

   xué​xí Hàn​yǔ xū​yào zhǎng​wò hěn​duō chéng​yǔ.

   Learning Chinese requires mastering many idioms.

   Source: Dong Chinese Dictionary

2. 这本书是目前最完整的成语大全。

   zhè běn shū shì mù​qián zuì wán​zhěng de chéng​yǔ dà​quán.

   This book is currently the most complete collection of idioms.

   Source: Dong Chinese Dictionary

3. 成语久假不归形容借了别人的东西长期不还。

   chéng​yǔ jiǔ jiǎ bù guī xíng​róng jiè le bié​ren de dōng​xi cháng​qī bù huán.

   The idiom 'jiu jia bu gui' describes borrowing something from someone and not returning it for a long time.

   Source: Dong Chinese Dictionary