When I (arrived/ had arrived), the train had left.
arrived
She went to bed after she (had done/ did) her homework.
had done
(When/ After) Mr Hassn arrived, the presentation had started.
When
Ali (had finished/ finished) his work by eight O'clock.
had finished
She didn't start cleaning until the children (left/ had left) for school.
had left
I (didn't see/ hadn't seen) Sara for a long time.
hadn't seen
(Could/ Will) I go out, please?
Could (ask for permission)
(Would/ May) you open your mouth, please?
Would (Make a polite request)
Majda (called/ had called) Salma before she went to work.
had called
(May/ Would) I help you?
May