我那会儿不知道这件事。

Wǒ nà huìr bù zhīdào zhè jiàn shì.

At that time I didn’t know about this matter.

那会儿你在做什么？

Nà huìr nǐ zài zuò shénme?

What were you doing at that time?

那会儿我每天都坐地铁去上班。

Nà huìr wǒ měitiān dōu zuò dìtiě qù shàngbān.

At that time I took the subway to work every day.