We use the Past Continuous to talk about a particular moment in the past.
· What were you doing at 9.30 last night?
· I was watching television. ( I was in the middle of watching TV at 8.30.)
We often use the Past Continuous and the Past Simple in the same sentence:
· They were cooking dinner when somebody knocked at the door.
(= They were in the middle of cooking dinner at that moment.]
· When Reena came to my house I was watching TV.
· I was teaching my daughter when Ravi came.