№3
1) Moscow
2) Moscow
3) Saint-Petersburg
4) Moscow
5) Saint-Petersburg
6) Moscow
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John and Sally visited the Russian museum in Saint-Petersburg last summer
John and Sally enjoyed the Summer Garden in Saint-Petersburg last summer
John and Sally had a boat trip in Saint-Petersburg last summer
John and Sally went to the circus in Saint-Petersburg last summer
John and Sally met Russian people in Saint-Petersburg last summer
John and Sally sent a postcart to their parents in Saint-Petersburg last summer
John and Sally wrote an e-mail to their friends in Saint-Petersburg last summer