Make one sentence out of two. Use the Past Perfect in

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.