2 sentences for 那天 (nà​tiān — that day)

1. 那天正好是他的生日。

   nà​tiān zhèng​hǎo shì tā de shēng​rì.

   That day happened to be his birthday.

   Source: Dong Chinese Dictionary

2. 你那天做了什么？

   nǐ nà​tiān zuò le shén​me?

   What did you do that day?

   Source: OpenSubtitles