past time clauses
Use:
Use the past perfect to talk about an action that took place before another action (in the past simple),
and link them with when or after. After we had eaten lunch, we relaxed on the beach for an hour.
Form:
The past perfect = subject + had + past participle
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Use:
Use the past simple to talk about an action happening while a longer one was in progress
(in the past continuous), and link them with when or while.
I was waiting at the bus stop when the two cars crashed.
Form:
The past continuous = subject + was / were + -ing form
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Language assistant
We use when to introduce either the shorter action or the longer one. We use while to
introduce only the longer one.