When the Twin Towers fell, I was eating some pizza and my mother was driving home from work
The PAST SIMPLE indicates finished actions and finished time. It also indicates a sequence of events, one after the other:
When I saw the news, I got up, looked at the TV and phoned my brother in New York.
Revise this point with this presentation:
simple past vs. past continuous
More PowerPoint presentations from Beth Bogage
For online exercises on the past simple go here and here. for exercises on the past continuous, go here and here.