4 sentences

1. 上课时千万不要分心。

   shàng​kè shí qiān​wàn bù yào fēn​xīn.

   Make sure not to get distracted in class.

   Source: Dong Chinese Dictionary

2. 别让他分心。

   bié ràng tā fēn​xīn.

   Don't distract him.

   Source: OpenSubtitles

3. 他做事非常专，从来不会因为杂事分心。

   tā zuò​shì fēi​cháng zhuān, cóng​lái bù huì yīn​wèi zá​shì fēn​xīn.

   He is very focused on his work and never gets distracted by trivial matters.

   Source: Dong Chinese Dictionary

4. 家里的事就请你多加分心了。

   jiā lǐ de shì jiù qǐng nǐ duō​jiā fēn​xīn le.

   Please look after the household matters for me.

   Source: Dong Chinese Dictionary