2 The children bought big ice-creams after they had climbed the top of St.Paul's.
3 The Tower became a popular tourist attraction after it had been a prison once.
4 After the group of tourists had came back from a boat trip, they took a taxi back to their hotel.
5 After David had worked in a factory for three years, he bought his taxi.
6. David hadn't had a job for a long time when he finelly decided to move to London.