Rita: got a minute?
Susan: Yep, what’s up?
Rita: need  help. Got test in English grammar tomorrow.
Susan: shoot.
Rita: what’s the main difference b’tween past simple and past continuous?
Susan: oh, c’mon, it’s trite.
Rita: oh yeah, smart ass? So?
Susan: Simple past describes complete past action and past continuous describes incomplete past action.
Rita: That’s it?
Susan: Yes, basically. Get the grammar book for the rest Good luck. 
Rita is having test in English grammar tomorrow.