Use: actions happening in the past
when something else happened or was happening.
past BE verb (was, were) + VERB-ing
She was baking a pie when I
left this morning.
the letter while watching the game. (was happening at the same time)
to the game when the accident happened. (was happening before)
Negative Form: was/were
I was not wearing pajamas
when the police came. I was wearing comfortable clothes.