When I arrived at the airport.I saw that  plane had taken off (plane/take off)
When Peter's mum asked him about his homework he said that he had done it  (he/do)
When they got to Ann's place all the guests had left  (all the guests/leave)
By the time I got home from school my grandma had cooked dinner  (my grandma/cook dinner)
When the teacher came into the classroom  pupils had learnt the results of the test (pupils /learn the results of the test)