Use the past continuous to express what was happening when something important happened. This form is almost always used with the time clause '... when xyz happened'. It is also possible to use this form with '... while something was happening' to express two past actions that were occurring simultaneously.
This tense is often used with the following time expressions:
... when xyz happened
... while xyz was happening.
Basic Construction
Positive
Subject + was / were + verb + ing + object(s) + time Expression
Sharon was watching TV when she received the telephone call.
Negative
Subject + was / were + not (wasn't, weren't) + verb + ing + object(s) + time Expression
We weren't doing anything important when you arrived.
Question
(Question Word) + was / were + subject + verb + ing + object(s) + time Expression
What were you doing when Tom gave you the bad news?
