这天 + Clause
这天 (zhè tiān) means "this day" or "on this day," used to refer to a specific day already established in a narrative. It helps set the scene for what happens next in a story.
这天早上,天气特别好。
Zhè tiān zǎoshang, tiānqì tèbié hǎo.
That morning, the weather was especially nice.
他永远忘不了这天发生的事。
Tā yǒngyuǎn wàng bù liǎo zhè tiān fāshēng de shì.
He will never forget what happened that day.
这天正好是她的生日。
Zhè tiān zhènghǎo shì tā de shēngrì.
That day happened to be her birthday.