2 sentences

1. 如果不经常练习，你的语言能力会逐渐退化。

   rú​guǒ bù jīng​cháng liàn​xí, nǐ de yǔ​yán néng​lì huì zhú​jiàn tuì​huà.

   If you don't practice regularly, your language skills will gradually decline.

   Source: Dong Chinese Dictionary

2. 由于长期在黑暗中生活，这种鱼的眼睛已经退化了。

   yóu​yú cháng​qī zài hēi'àn zhōng shēng​huó, zhè zhǒng yú de yǎn​jing yǐ​jīng tuì​huà le.

   Due to living in darkness for a long time, the eyes of this fish species have degenerated.

   Source: Dong Chinese Dictionary