3 sentences

1. 她在帮我钉掉落的纽扣。

   tā zài bāng wǒ dìng diào​luò de niǔ​kòu.

   She is helping me sew on a button that fell off.

   Source: Dong Chinese Dictionary

2. 我喜欢你的纽扣。

   wǒ xǐ​huan nǐ de niǔ​kòu.

   I like your buttons.

   Source: OpenSubtitles

3. 我这件衬衫掉了一个纽扣。

   wǒ zhè jiàn chèn​shān diào le yī gè niǔ​kòu.

   A button has come off my shirt.

   Source: Dong Chinese Dictionary